There is nothing you can do about his parents right now. If you get the house yes you can ask them to move. That is not likely to happen.
Children has custody, visitation, support etc needs to be addressed.
Property will be divided. (I am not familiar with CA. I am in NV) In Nevada, generally we do 50/50. No fault state.
My advise is that get a lawyer and dont try to save penny and end up lose a lot more than you can imagine.