Depends. If the quarrel topic is about the children, then she should let them learn. But if the topic has nothing to do with children or not reasonable, then she is doing something really good to protect them.
Wait she is rescuing the kids or the hubby? If it’s the kids, she prob just dotes on them too much
If you dont agree with your in laws, distant yourself from them as much as possible
You can tell your mil nicely to respect you guys.
Not very nice. Should let you two handle it