My example does not assume constant control by a family member. You just need the voter to be under your control at the time electronic voting ends. Or, even simpler, for them to give you their credentials for electronic voting, so *you* can vote for them at the end of the allotted time.
Yes, this example requires a party representative to be on the board. I am not sure which threat model you have, but to me this seems the most dangerous scenario, not individual efforts to coerce one single vote.
Yes, I agree that paper voting has its drawbacks, too, and cameras are an important loophole. But checking if a person goes to the polls or not seems simpler than giving them a camera, at least in my view. I assume the voting officials keep records of who goes to the polling station, and that party representatives can audit them.