Wow, that's a tough one.
I'm super lucky, I have the best in-laws. We (DH, me, DD, MIL, FIL, SIL, her hubby, and their 4 kids) all went for Halloween, and we don't see them much, we live across the country from them. It was my daughter's first trip, and my hubby told my In-laws way before we even left, that we were not spending every second together (mostly due to how SIL and her family do trips there), that this was OUR vacation too and there were things we wanted to do. We came to a nice compromise. We spent some time with SIL and her kids, but not a ton. We had Halloween night with them, and Josie's b-day dinner and a morning together before they went home. Then, we would spend the days with my MIL and FIL, then they went back to their room to rest in the afternoons, and we had the rest of the day and dinner to ourselves. Some of my favorite pictures are Josie with my MIL.
We had a wonderful time, and my hubby was the one who would get annoyed with his family, not me.
Even though things are smooth with them, my family can be difficult at times. But, I know that my hubby comes first. When I married him, he (and later DD) became my family. All the rest of our families are the secondary family.
And, I think you need to tell your hubby this. He is your partner, it is your life together. MIL can offer advice on your life, but she has no real say in it. You and your hubby are a team, you need to make the decisions for yourselves, by yourselves. You need to set guidelines now, or things will only get worse.
Have you explained to your hubby how you feel? IMHO, you really need to sit down, and get him on your side. I really like how the PP's said that this would be her vacation with her family, and you would be the guest, standing off to the side. These are your kids, you ned to be able to plan their trip, and do things your way. Bring up her previous behavior with money, and how she would do the same with this trip, and that if he does not make a stand now, he'll be caught in the middle of you two (and the control struggle) for the
rest of his life. Get him to realize that though he may not care, it really upsets you. He needs to put you, and YOUR family first, and not just let her steamroll you both because it's what he's used to. Deal with the stress of standing up to her now, and it will be easier down the road. To quote another poster here "Tell him to grow some Mickeys".
OK, I'm getting off my soapbox now.