My sympathies to you! I have dealt with crazy, drama-loving in-laws for almost 11 years now. It is always stressful to deal with 'cause you need to be able to be civil to them so as to avoid putting a strain on your marriage. :\
In the past, I have refused to go to holiday gatherings with his side of the family, and while that kept me from stressing out and getting upset, it made my hubby resent me for it. My advice to you would be to suck it up if you can and be around them, even if it makes you unhappy for a little while... It's up to you to decide if a happy marriage is worth it. 😉