One component on top of the other

Android already has a layout that makes your children overlap, is FrameLayout , replace RelativeLayout with it like this:

<FrameLayout
   ... // width, height e tudo do RelativeLayout aqui>

<LinearLayout
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:background="#00008B"/>

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:background="#008B45"/>

</LinearLayout>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:elevation="@dimen/activity_vertical_margin"
    android:text="CHAPÉU SELETOR"
    android:textColor="#FFFFFF"
    android:textSize="40sp"
    android:gravity="center_vertical"
    android:layout_gravity="center"
    android:id="@+id/textView"/>

<Button
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Testar"
    android:textSize="40sp"
    android:id="@+id/buttonStart"
    android:background="#FFFFFF"
    android:layout_gravity="center" />

</FrameLayout>

With this Layout the elements will already overlap. Any questions just comment.

Try it out like this, it might work !!

If it does not work, tell me to try another way

<FrameLayout
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" >

    <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:elevation="@dimen/activity_vertical_margin"
            android:text="CHAPÉU SELETOR"
            android:textColor="#FFFFFF"
            android:textSize="40sp"
            android:gravity="center_vertical"
            android:layout_centerVertical="true"
            android:layout_centerHorizontal="true"
            android:id="@+id/textView"/>

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Testar"
            android:textSize="40sp"
            android:id="@+id/buttonStart"
            android:background="#FFFFFF"
            android:layout_below="@+id/textView"
            android:layout_centerHorizontal="true" />
    </FrameLayout>

I'm sorry, I solved the case by changing the order, putting the textView and Button at the end of RelativeLayout, I had posted the code this way, but in my project I do not know why I had undone this put the textView and the Button at the beginning of the code. Now everything went well, thank you all for the answers, thank you

Invert the order of the code.

On Android the order of factors changes the product :) If not, I've changed the emulator and see if it works.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.uriel.aaa.MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:elevation="@dimen/activity_vertical_margin"
        android:gravity="center_vertical"
        android:text="aaa"
        android:textColor="#FFFFFF"
        android:textSize="40sp" />

    <Button
        android:id="@+id/buttonStart"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView"
        android:layout_centerHorizontal="true"
        android:background="#FFFFFF"
        android:text="Testar"
        android:textSize="40sp" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:orientation="horizontal">


        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:background="#00008B"
            android:orientation="horizontal" />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:background="#008B45"
            android:orientation="horizontal" />
    </LinearLayout>

</RelativeLayout>

Hello. The contraintLayout is what I use most, and there, the order of the factors can overlap yes.

        <RadioButton
            android:id="@+id/radioButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_alignParentStart="true"
            android:layout_weight="1"
            android:background="@color/fbutton_color_clouds"
            android:checked="false"
            android:text="Bloco 40 cm"
            android:textAlignment="viewStart"
            android:textColor="@color/fbutton_color_wet_asphalt"
            tools:layout_editor_absoluteX="152dp"
            tools:layout_editor_absoluteY="484dp" />

        <RadioButton
            android:id="@+id/radioButton2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:background="@color/fbutton_color_clouds"
            android:checked="false"
            android:duplicateParentState="false"
            android:text="Bloco 33 cm"
            android:textColor="@color/fbutton_color_wet_asphalt"
            tools:layout_editor_absoluteX="27dp"
            tools:layout_editor_absoluteY="484dp" />

    </RadioGroup>



    <TextView
        android:id="@+id/textView5"
        android:layout_width="185dp"
        android:layout_height="103dp"
        android:layout_alignParentTop="true"
        android:layout_weight="1"
        android:text="Os blocos de EPS podem ter  40cm ou 33cm de largura. Escolha o que irá ser utilizado"
        android:textAlignment="center"
        android:textColor="@color/colorPrimary"
        android:textSize="14sp"
        app:layout_constraintTop_toTopOf="@+id/radioGroup2"
        tools:layout_editor_absoluteX="149dp" />