How can I get controlling family members to compromise with me?

Okay, so I have a cousin and her niece coming over and I have agreed to take them down to LA and take them down to Anaheim (Disneyland) before they have to leave. Well, ever since my aunts, cousins, and grandma found out, they want to take control now! My cousin told them my plans of what I was going to do with them, and now a cousin of mine, (not the ones visiting) wants to do just that and she just decided that I'm not going with them! "Are you seriously kidding me!?" I thought. I seriously don't know how to react to this or what to do, how pissed off I am. I know better than to get mad with them, because that's EXACTLY what they want. They feed off people's anger and laugh at them (that's the type of people they are.) They even "banned" me from going to San Jose to pick them up, because I "have no experience" in driving up there. I'm just so furious right now.