Stuck on styling a taskstack toolbar on the launched activity

AndroidManifest.xml

...
    <application
        android:name=".MyApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:screenOrientation="portrait"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".activities.MainActivity"
            android:label="@string/app_name"
            android:screenOrientation="portrait"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".activities.RegisterActivity"
            android:theme="@style/AppTheme"
            android:label="@string/menu_register"
            android:parentActivityName="io.getstream.example.activities.MainActivity"
            android:screenOrientation="portrait"
            android:windowSoftInputMode="stateHidden" />

...

main_layout.xml

<?xml ...>
<android.support.design.widget.CoordinatorLayout ...

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:popupTheme="@style/ToolbarPopupOverlay" <!-- is this even needed? -->
            android:theme="@style/ToolbarTheme" />

    </android.support.design.widget.AppBarLayout>
    </android.support.design.widget.AppBarLayout>

...
</android.support.design.widget.CoordinatorLayout>

...

MainActivity.xml

    protected void launchActivity(String activity, Context context) {
        intent = null;
        int requestCode = 0;

        if (activity.equals("register")) {
            requestCode = CONST_ACTIVITY_REGISTER;
            intent = new Intent(context, RegisterActivity.class);
        } else { ... }

        if (intent != null) {
            TaskStackBuilder taskStackBuilder = TaskStackBuilder.create(this);
            taskStackBuilder.addParentStack(MainActivity.class);
            taskStackBuilder.addNextIntent(intent);

            PendingIntent pendingIntent = taskStackBuilder.getPendingIntent(0, PendingIntent.FLAG_ONE_SHOT);

            NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
            builder.setContentIntent(pendingIntent);

            startActivityForResult(intent, requestCode);
        }
    }

Why are you using 2 AbbBarLayout anyway?