God Bless you Zual,
You are stronger than you think. You are a mighty woman of God fighting for your family. He will give you strength to hold on- Don't try to fight your battles-calmly explain once like you did above. God will vindicate you and your sensible, calm and loving behavior toward him as opposed to his fruitcake sister (forgive me, Lord) will convince him.
For the kids sake have them go to family functions with him. Stay home and treat yourself-bubble bath, ice cream, chocolate a movie, do your nails, a walk, all of the above, whatever your special little pleasure is (maybe just the joy of having to house to yourself) give yourself a treat, Princess-You deserve it!!!!
Try to never speak negatively because they are the kid's gramma,grampa, aunt, uncle, ect. amd you know they love the kids. Meanwhile, your kids will have the example of a godly mother to follow and will respect you. God will cause your husband to fall in love with you all over again. Be gentle, be his refuge from stress. He must hate the fighting, too. He might be embarassed about how his faimily is behaving but can't admit it. So have him open up a jar for you and he opens up that jar for you, flutter your eyelashes and give him the old "Thank you, you're so stroooong" like ya did when you guys started dating. He'll still fall for it. My husband is 63 and he still does
Most important pray, pray, pray for him, the kids, for them. I'll pray too. Read the Psalms-David poured his heart out, I'm sure you'll find comfort and hope.
Your Sister is Christ
Proverbs 31:25 Strength and honor are her clothing and she shall rejoice in time to come.