I'm in your shoes. You have to find a way to emotionaly disconnect from your in-laws. You didn't marry them you married their son. Some mother in laws can be annoying, but you can't control what they do. You can only control how you react. I don't think it's worth breaking up the marriage over.
At the same time, those are his parents and they are going to be in your lives somehow. When familles merge it's hard to adjust and accept others. I had to realize that. My in-laws aren't like my parents and never will be. They dont hold a candle to them. But they are my husbands parents so I have to respect that. But at the same time you are entitled to set up your own traditions and routines that they should abide by. I know you said they want to come when they come so I'm sure that can be tough.
Your husband is caught in the middle and is being pulled in two directions. I agree that he should side with you. He doesn't have to always agree with you but he should show open support since you are his wife. When they side with their parent's in front of you it does suck and I swear the mother will gloat. Just go about your day and your life with your family. Don't let them ruin your marriage. If they choose not to come when invited then that's their issue not yours. In-laws always try to pull rank to show that they are more important than you. Stupid I know, but that's what they do.
Pick your battles. They are going to do A LOT of annoying things so choose wisely. If they want to give gifts let em. I was annoyed that my in-laws bought so many clothes for my daughters then I was like wait - I could use these clothes! So i wouldn't put too much energy into the gifts. They are trying to incorporate themselves into your family nucleus. They can't do that. Your husband needs to step up and let you be a nucleus family and everyone outside that should respect it. It took FOREVER!!!! to get their with my in-laws.
Also, please keep in mind that no one is perfect and he's only human so he of course would be affected having his wife and parent's not get along. Focus your energy on him. Be super sweet. I find that when I'm like that with my husband he's more in-tune with me when things go awry. Tell him that you understand that he's caught in the middle, but you love him and don't want anything to break up your family. Just be wifey 101 with him. So when it's time to "battle" with your in-laws he'll be more inclined to stand by your side.
Take the energy off your in-laws and put it towards your family.