Is it possible to add TextView below RadioButton in RadioGroup in any other way than extending and creating my custom RadioButton?
Yes, its possible. See below:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<RadioGroup
android:layout_width="fill_parent"
android:layout_height="wrap_content" >
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="btn1" />
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="btn2" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="sample text" />
</RadioGroup>
</LinearLayout>
Sample output: