Overriden activity capable of inflating child fragment tags in fragment xml layouts. This activity will successfully use the ChildFragmentManager of the parent fragment. At the bottom of the gist is a custom attr definition. For your child fragment defined in xml you'll be definining the parent fragment name.

gistfile1.java

package com.project.floatingvideos;

import java.util.Random;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.view.View.OnAttachStateChangeListener;
import android.widget.FrameLayout;

public abstract class ChildFragmentActivity extends Activity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
	}

	@Override
	public View onCreateView(final View parent, String name, final Context context, final AttributeSet attrs) {
		TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.fragment);
		final String parentFragmentName = a.getString(R.styleable.fragment_parent);
		a.recycle();
		if ("fragment".equals(name) && parentFragmentName != null) {
			// Ensure a unique container id
			final int containerId = getUniqueContainerId();
			final String fragmentClass = attrs.getAttributeValue(null, "class");
			// Add a container for the child fragment to the layout
			//When that layout is attached add a child fragment to it using the ChildFragmentManager
			//of the parent fragment specified by the parent attribute
			final FrameLayout container = new FrameLayout(context);
			Log.d(ChildFragmentActivity.class.getSimpleName(), "Child fragment to be inflated pending container attachment to window: " + fragmentClass);
			container.addOnAttachStateChangeListener(new OnAttachStateChangeListener() {
				@Override public void onViewDetachedFromWindow(View v) {}
				@Override
				public void onViewAttachedToWindow(View v) {
					Log.d(ChildFragmentActivity.class.getSimpleName(), "Container attached to window, inflating fragment: " + fragmentClass);
					container.removeOnAttachStateChangeListener(this);
					try {
						Fragment parentFragment = getFragmentManager().findFragmentByTag(parentFragmentName);
						if (parentFragment == null)
							throw new IllegalStateException("Parent fragment unavailable");
						Fragment childFragment = Fragment.instantiate(context, fragmentClass);
						FragmentManager fragmentManager = parentFragment.getChildFragmentManager();
						FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
						fragmentTransaction.replace(containerId, childFragment, fragmentClass);
						fragmentTransaction.commitAllowingStateLoss();
					} catch(IllegalStateException e) {
						e.printStackTrace();
					}
					
				}
			});
			container.setId(containerId);
			return container;
		} else if (!"fragment".equals(name)) {
			return onCreateView(name, context, attrs);
		} else {
			Log.d(ChildFragmentActivity.class.getSimpleName(), "Parent fragment being loaded");
			return super.onCreateView(parent, name, context, attrs);
		}
	}

	private int getUniqueContainerId() {
		int containerId;
		do {
			containerId = new Random().nextInt(1000);
		} while (findViewById(containerId) != null);
		return containerId;
	}

	@Override
	public void onAttachFragment(Fragment fragment) {
		super.onAttachFragment(fragment);
		Log.d(ChildFragmentActivity.class.getSimpleName(), "Parent Fragment Attached: " + fragment.getClass().getName());
	}
}


//You need your custom attribute

//    <declare-styleable name="fragment">
//        <attr name="parent" format="string"/>
//    </declare-styleable>	

//Use the attribute on your intended child fragment
//app:parent="com.paltalk.chat.room.fragments.RoomDetailsFragment"