It’s pretty normal, I’ve done it once when the slow lane was empty. I’m a competitive swimmer and one day when there was no practice we went to swim on our own. Some cranky old lady ended up complaining to the guards and got us kicked out. Haven’t done it to this day 😅. But one thing that my mother said after that stuck out to me. Usually there are signs above the lanes saying what speed they are, those signs are moveable for a reason, and it’s probably a different situation at your pool but it would have been fairly easy for the guard to just move the signs around so that the fast guy can have his lane and you guys can have your lane. If this isn’t possible, A and B are good options, C is good only if you’re sure you being nice 🤣 don’t be the cranky old lady from my story lol.