Anyone not listed is not supposed to use the amenities…doesn’t matter if they don’t sleep there. If you have room, just add them.
If they are staying at a different WDW resort, then add them using middle names so it doesn’t link to their
MDE. This way, they have the right to use the pool.
if you aren’t going to do that, and Just have to visit the villa, then it’s not necessary. BCV is especially strict since you have to get the wrist bands and without being listed, they won’t get in to that pool.