@kimmjohns I would suggest that you and your husband are on the same page. If you both do NOT want to go you both are going to need to be a United front. You can say NO all day long, but if your MIL can go behind your back and wear down your husband. Then No isn’t going to mean NO and she knows this.
Talk to your husband, tell him what you want. Aka “I do not want to go on a whole family vacation with your family.” If he wants to go, see if you can compromise like he takes the kids, you stay home, or you guys stay in your own hotel room away from them and only join them for events that you guys want to.
Once you are both on the same page the both of you need to tell MiL THE plan. I say both of you, because your husband doesn’t have enough of a spine to stand up to his mother yet, your job is to keep her from wearing him down. With “MIL this is what WE are going to do, We are not changing OUR plans.” Showing her you two are a United front needs to be top priority. Because right now she bullies your husband to force your hand. There needs to be no debating, no we will see what she wants. You two make the plan and MIL gets to stick to it. End of discussion.
Once it is all said and done stick to your guns, no matter how much she and your in laws may rage. Don’t let your husband change the plan, if that means he needs to ignore his family for a bit so be it.
You are both adults, married, and parent, if you both don’t start demanding to be treated as such your MIL will continue l to boundary stop, until her dying breath.