You prob can't rent a hotel room, most places you have to be at least 21. Unless it's really sleazy and then she probably would feel like a whore!
Yep, if your dad is cool with you guys having sex there, then it shouldn't be a problem to just let him know the sign to look for that says "don't bother me, I'm fucking". Ummm... sorry, "making sweet, sweet love" I mean.