Can I change locks on our apt in our 2 family home and send husband to upstairs unit where his mother lives?

Assuming you both own the house equally, you cannot evict him without a court order. You can go to Family Court and try to get a restraining order preventing him from being in your house if you have proof that he stole from you and are afraid he will continue to steal. You can also go to Supreme Court and start a partition action against him which essentially asks the court to divide the house in half. Although that rarely happens, in this case it actually could (although your mother-in-law's presence complicates things). The other possible result of a partition action is a sale of the house and the division of the proceeds. It would be best for you to buy him out, if you can. But a partition action really makes no sense if you're starting a divorce action, because the house is marital property subject to dispositon in the divorce action. You may eventually get the whole house in a divorce action, depending on all the other factors involved, but divorce and division of marital property don't happen quickly unless both parties agree to the terms of the divorce quickly.