Spinner alignment can be done to parent, its just need to repeat margins on second one

spinner_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="265dp"
        android:scaleType="fitXY"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0"
        tools:ignore="ContentDescription" />


    <!--    app:srcCompat="@mipmap/comment"-->
    <ImageButton
        android:id="@+id/commentButton"
        android:layout_width="100dp"
        android:layout_height="50dp"
        android:background="@null"
        android:contentDescription="comment_Button"
        android:scaleType="fitCenter"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.87" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="comment"
        android:textSize="18dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.025"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.8" />


    <!--    android:background="@drawable/custom_button"-->
    <!--    android:text="@string/order_Button"-->
    <Button
        android:id="@+id/ordering_button"
        android:layout_width="163dp"
        android:layout_height="72dp"

        android:textAllCaps="false"
        android:textColor="#121212"
        android:textSize="25sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.885" />


    <!--    app:menu="@menu/bottom_navigation"-->
    <!--    android:background="@color/colorGreen"-->
    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:itemIconTint="@color/colorPrimaryDark"

        app:itemTextColor="@color/colorAccent"
        app:labelVisibilityMode="labeled"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />


    <TextView
        android:id="@+id/tvName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

        android:gravity="center"
        android:textColor="#000000"
        android:textSize="29sp"
        android:textStyle="bold"
        app:fontFamily="casual"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.489"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.41" />


    <!--    android:text="@string/size"-->
    <TextView
        android:id="@+id/textViewS"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

        android:textColor="#000000"
        android:textSize="20sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.025"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.481" />

    <!--    android:text="TextViewB"-->
    <TextView

        android:id="@+id/textViewB"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#000000"
        android:textSize="20sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.025"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.642" /><![CDATA[

    />


    ]]>


    <RadioGroup
        android:id="@+id/radioGroup_Size"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.862"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"

        app:layout_constraintVertical_bias="0.485">


        <!--        android:background="@drawable/background_selector"-->
        <!--        android:text="@string/small"-->
        <!--        android:textColor="@drawable/text_selector"-->
        <RadioButton
            android:id="@+id/r_Button_Small"
            android:layout_width="95dp"
            android:layout_height="35dp"
            android:layout_marginLeft="50dp"

            android:layout_weight="1"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.322"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />


        <!--        android:background="@drawable/background_selector"-->
        <!--        android:text="@string/Medium"-->
        <!--        android:textColor="@drawable/text_selector"-->
        <RadioButton
            android:id="@+id/r_Button_Medium"
            android:layout_width="95dp"
            android:layout_height="35dp"
            android:layout_marginLeft="10dp"
            android:layout_weight="1"

            android:checked="true"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.962"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <!--        android:background="@drawable/background_selector"-->
        <!--        android:text="@string/Large"-->
        <!--        android:textColor="@drawable/text_selector"-->
        <RadioButton
            android:id="@+id/r_Button_Large"
            android:layout_width="95dp"
            android:layout_height="35dp"
            android:layout_marginLeft="10dp"
            android:layout_weight="1"

            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.962"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

    </RadioGroup>


    <!--    android:background="@color/md_teal_800"
    android:entries="@array/days_of_week" -->
    <!-- //user8608556   Both spinner1 & 2 layout_width make 0dp to set in constraint added marginStart & end, change as per need -->
    <Spinner
        android:id="@+id/spinner1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="50dp"
        android:layout_marginEnd="50dp"
        android:popupBackground="#5fe0f5"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.59"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.645"
        android:entries="@array/days_of_week"/>

    <!--    android:background="@color/md_teal_800"
    android:entries="@array/days_of_week_options"-->
    <!-- //user8608556   //spinner2 start & end align to spinner1 so just margin on spinner1 will do the trick-->
    <androidx.appcompat.widget.AppCompatSpinner
        android:id="@+id/spinner2"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:popupBackground="#5fe0f5"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.59"
        app:layout_constraintStart_toStartOf="parent"
        android:layout_marginStart="50dp"
        android:layout_marginEnd="50dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.723"
        android:entries="@array/days_of_week_options"/>

    <!--    android:text="TextViewC"-->
    <TextView

        android:id="@+id/textViewC"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#000000"
        android:textSize="20sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.025"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.72" />


</androidx.constraintlayout.widget.ConstraintLayout>

You can align spinner2 to parent instead of spinner1, it just you have to repeat the margins. Moreover in future you change alignment of spinner1 you need to do so on spinner2 with this approach(As you wanted both aligned below another). It sort of small code maintainability :)