Your android.support.v4.app.FragmentTabHost
has a height of MATCH_PARENT and therefore the layout at the bottom will not appear.
One alternative would be using a RelativeLayout to create the header/content/footer layout:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<include android:id="@+id/header"
android:layout_alignParentTop="true"
layout="@layout/screen_parent_topbar" />
<include android:id="@+id/footer"
android:layout_alignParentBottom="true"
layout="@layout/screen_parent_bottombar" />
<android.support.v4.app.FragmentTabHost
android:layout_below="@id/header"
android:layout_above="@id/footer"
android:id="@android:id/tabhost"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<FrameLayout
android:id="@+id/tabcontent"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</android.support.v4.app.FragmentTabHost>
</RelativeLayout>