Is it rude to ask someone to go swim in their pool?

you should wait to be invited.

Since it was already offered to you, it's not only not rude but it's very polite that you would ask first.

Not at all.

You're right to be cautious, because sometimes people do without thinking issue invitations that they don't really mean. Check with your dad; they are his friends and he should have a better feel for whether they likely meant it or not.

And if he says it's OK to ask, make it specific: 'would it be OK if we came to swim next Wednesday afternoon?' Then, if they really didn't mean to invite you, they can just say 'sorry, that's not convenient' without embarrassment to anyone. If they did mean to invite you but that day really isn't convenient for them, they can always say 'Sorry, not Wednesday, but Thursday or Friday would be fine, we'd love you to come!' So you'll be able to judge by their response how welcome you might be. (Suggesting specific dates is a very good approach to adopt in general when you aren't 100% sure of the other person's feelings; a vague suggestion to do X together 'sometime' forces them either to say outright 'No, I don't want to do X with you ever' or, if they don't feel brutal enough to do that, accept when they really don't want to.)

No, since they proposed it themselves first! It's only polite and nothing is bad at this.

Have your dad ask

I have had pools

Always bring your own towels..

Bring your own drinks

take your towels and bottles with u when you leave

move furniture back to where it was when you got there

its not rude, but he already said you could

No...they have given you permission to.

no

Hmm! Nope!