How should I have a pool party for my class if it's not my house, and in a different town.?

I want to have it at my dads house. He has a pool, a big backyard, and a meadow behind it. He has lots of bikes, floaties, a deck, couches on the deck along with a table. A hammock, sprinklers, and in the house he has a flat screen TV. How do I go about having my party there when my aunt and uncle own the house and 3 year old cousin lives there, but so does my dad?