Wisconsin Divorce Law Question?

My mom is divorcing my step dad. He isn't a nice guy and has done somethings wrong like sexual assault and actually gotten fired for sexual harassment at work 3 times in the past year. My mom has 5 kids to take care of and has Multiple Sclerosis so we don't want to move. I know that WI is a 50-50 state and all property is to be split evenly. Is there any way that my mom could get out of having to buy him out for the house? And if there isn't, how would it work if what the house is valued at right now is less than the mortgage still owed on it?