Seek a marriage counselor asap. Go to your masjid Imam even and talk it out in front of him.
MILs are nothing to deal with if and when the relationship between husband and wife is strong.
You have children that will soon grow up and see this. The negativity WILL transfer over into their lives.
One more thing: Marriage is not supposed to be lived as a punishment. Yes, sometimes there will be stages when “nibhana” is more important than anything else. However, the overall relationship is still healthy and able to conquer those periods of negativity. If you’re married, living with someone 24/7, sharing a life with them, have kids with them, etc., you might as well find a way to make it work for you. You might as well find the source of his unhappiness and see if you can do anything about it to relieve the atmosphere in your home.
Good luck 