L.W.
Let them know in no uncertain terms that you will NOT stand for their being disrespectful to your husband in your presence. In the words of Loretta Lynn, "Stand by Your Man". If they can't refrain, reprimand. If that doesn't work, withdraw from the family circle. Not forever, but definitely limit the times to holidays or something. They will get the message you are serious. Also, if they belittle your DH in the presence of your children, their opinion of their dad will be less. That would be a very serious situation; it should be addressed immediately!