Family dilemma, needing advice.?

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.

Our siblings seem to have the idea that if we're in town, then we are free sitters for their kids "so cousins can play".

Siblings always figure out a way ditch out - they go shopping, movies, out to dinner (without us!).

Don't get me wrong, I adore my nieces & nephews, but their ages are 2-8, so they're not exactly self-sufficient.

I earn my time off work - only to use it working. And I'm beginning to despise the idea of visiting.

We've tried talking to the siblings adult-adult, which resulted in them only being more calculated in ditching. "Just need to run to the store for milk", "friend ran out of gas", "need to step out & make a phone call" (and disappear for hours).

We are heading over next week, when kids get out of school for summer. We haven't visited since before holidays, and parents have all but begged us to come.

Advice??