Is there a way to turn video on iPhone to phone speaker from hearing aid like you can on phone app

You can pause the YouTube playback, go to settings and turnoff bluetooth for the playback to your speakers on your iPhone and when finished go to settings and turn bluetooth back on. This way you are not messing with your Accessibility Hearing Devices settings.

Yes, you should be able to tap the screen on a FaceTime call and switch audio output to speaker just like on a voice only call.