Your wife co signed for her son a loan if he defaults can they come after property she and you have jointly even though you did not co sign?

Short answer, yes. Even though you are on the property jointly, she is a responsible party on the cosigned loan. As such, she owns the cowned property same as you. If you own a car together, for instance, she owns as much of the car as you do. It is her car. It is still your car, but for the purposes of securing satisfaction for the eventual judgment on the other loan, she owns the car.