Yikes. That's a lot of work. Litchi has screen recorder as well for iOS. Now let me think. You overlay in iMovie. Think the only problem is we can't really see the data from the overlay being so small. I will give you example of litchi overlay. But I lost my original sound when I uploaded it. Interesting also. I'm using windows movie maker. Not sure how you did the overlay as well from that. Hmmunfortunately i think this is pretty hard to do on an ipad. it was a pain and i ended up selling my ipad mini 4 as a result of frustration and went back to using my nexus 9.
i use a free app on android to record the screen. i overlay the screens in iMovie and export to a 4k video and upload the video to youtube. it's pretty easy to do overall but these are 2 different video files so it can be a bit of a pain to sync them.