Thanks for posting and linking the videos. I'm guessing you'll get lots of (more-seasoned) responses, but here are my takes as someone who just completed their third season. All of these assume NCAA rules as applied in Texas HS.
For the FG: the umpire is indicating that the kick was tipped, but a blocked scrimmage kick that's blocked within 3 yards of the NZ is considered to be untouched by B, so the proper spot would be the B21, not where it was downed.
For the three plays: the first play is close, but the back's action is not a jerky, sudden movement designed to simulate the start of the play, and since he doesn't move his feet it's hard to really call illegal motion either. I have nothing on that play, but would probably try to talk to the player or the coach as I agree it is close. On the second play, I definitely have A44 covered up and then downfield. On the third play, I don't see a false start by the back at all (I assume you're referring to the back closest to the press box sideline?). I watched several times, and if you have to do that to decide if there's a foul, it's probably best not to call one.