My son in law is going through a divorce and his wife is trying to keep the house that they built together and he just fired his attorney.

Under Wisconsin law, all property acquired either before or during the marriage is presumptively equal. The only exception is gifted or inherited property acquired from a third party. The home they built together is marital. The home should be appraised by agreement or by an order of the court to determine its' value. The equity is determined by fair market value (appraised value) - the current mortgage loan payoff. If that number is $200,000 by example, to keep the house she would have to pay him $100,000 and be required to refinance the mortgage into her name only so title and the mortgage can both be cleared. If they are both fighting for the house, chances are at trial, the court very well may simply order that the house be sold.       If they have minor children, the court can consider as a  factor letting the parent with  primary placement to stay in the home to take care of the children.