Family dynamics/dilemma?

My husband & I live a state away from any family (work relocation). So we don't get to visit family very often, and when we do - it always digs in to our vacation time off. Rarely do we use time off for anything else.

We love seeing family, our kids adore their cousins & aunts/uncles, grandparents...

I'd like to think we've maintained close family ties.

However, the dilemma kicks in when we turn into babysitters on our own time off. Cousins are always ditched on us, our car can't hold more than our own little family, so essentially we get stuck at someone else's house with a bunch of kids on our "vacation".

We have tried speaking to our brothers & sisters about it, but they've only gotten more calculated in dropping off their kids. They interrogate in advance when we're leaving, where we'll be staying (usually mom & dad's house)... - and usually have their kids dropped off early so they don't have to talk to us. Basically ditching them with grandma until we arrive.

My nieces and nephews are no longer enjoyable to be around, because we've turned into the disciplinarians. We rarely see our siblings anymore because it seems they are avoiding the very conflict they have created.

We have the oldest child in the group (11), and ages af all the kids range down to 2 years old. These are not self-sufficient children here. They take a lot of work & I loathe the idea of working on the vacation that I've already worked to earn.

We are heading over next week, any advice out there?