You have to focus on RelativeLayout.
MyActivity.java
public class MyActivity extends Activity {
private RelativeLayout mainLayout;
private TextView myTag;
private TextView xcordview;
private TextView ycordview;
private MediaPlayer mp1;
private String currentTag;
private boolean areaDetected;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_my);
    mainLayout = (RelativeLayout) findViewById(R.id.main_layout);
    myTag = (TextView) findViewById(R.id.tag);
    xcordview = (TextView) findViewById(R.id.x_view);
    ycordview = (TextView) findViewById(R.id.y_view);
    currentTag = "";
    initEvent();
}
private void initEvent() {
    mainLayout.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View view, MotionEvent motionEvent) {
            int x = (int) motionEvent.getX();
            int y = (int) motionEvent.getY();
            xcordview.setText("X : " + String.valueOf(x));
            ycordview.setText("Y : " + String.valueOf(y));
            areaDetected = false;
            for (int i = 0; i < mainLayout.getChildCount(); i++) {
                View currentButton = mainLayout.getChildAt(i);
                if (currentButton instanceof Button) {
                    Button b = (Button) currentButton;
                    String tag = b.getTag().toString();
                    if (!pointInside(x, y, b.getLeft(), b.getRight(), b.getTop(), b.getBottom())) {
                        b.setText("");
                        // b.setBackgroundResource(getResources().getColor(android.R.color.black));
                    } else {
                        areaDetected = true;
                        if (!currentTag.equals(tag)) {
                            currentTag = tag;
                            stopPlaying();
                            b.setText(tag);
                            mp1 = getMediaPlayer(tag);
                            mp1.start();
                            // b.setBackgroundResource(getResources().getColor(android.R.color.white));
                        }
                    }
                }
            }
            if (!areaDetected) {
                currentTag = "";
                stopPlaying();
            }
            myTag.setText("Current tag : " + currentTag);
            return true;
        }
    });
}
private void stopPlaying() {
    if (mp1 != null) {
        mp1.stop();
        mp1.release();
        mp1 = null;
    }
}
private MediaPlayer getMediaPlayer(String tag) {
    if (tag.equals("b1")) {
        return MediaPlayer.create(MyActivity.this, R.raw.coffee_and_snow);
    }
    return MediaPlayer.create(MyActivity.this, R.raw.coffee_and_snow2);
}
static boolean pointInside(int x, int y, int x1, int x2, int y1, int y2) {
    return (x <= x2 && x >= x1 && y <= y2 && y >= y1);
}
}
and the xml file
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MyActivity">
    <com.example.antoine.touchtest.MyButton
        android:id="@+id/b1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:tag="b1" />
    <com.example.antoine.touchtest.MyButton
        android:id="@+id/b2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/b1"
        android:tag="b2" />
    <com.example.antoine.touchtest.MyButton
        android:id="@+id/b3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/b2"
        android:tag="b3" />
    <com.example.antoine.touchtest.MyButton
        android:id="@+id/b4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/b3"
        android:tag="b4" />
    <TextView
        android:id="@+id/x_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/y_view"
        android:text="X : " />
    <TextView
        android:id="@+id/tag"
        android:layout_above="@+id/x_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Current tag : " />
    <TextView
        android:id="@+id/y_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:text="Y : " />
</RelativeLayout>
Finally my custom button
MyButton
public class MyButton extends Button {
    public MyButton(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub
    }
    public MyButton(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
    }
    public MyButton(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        // return super.onTouchEvent(event);
        return false;
    }
}
A big thanks to this post ==> Get button coordinates and detect if finger is over them - Android