My marriage is on the rocks.. I just recently bought a house and her parents co-signed. They are the primary and I'm the secondary signer. I am paying the mortgage with my income and my wife's part-time income. She has claimed that if we divorced her parents have said they would take their name off the title. Is that even possible and what are my options as the second signer?

A co-signer is not necessarily on the title. If they are on the title they are a part owner and the mortgage lender is not going to allow them off the title and definitely not off the mortgage unless you refinance.

We are both on the title deed. So what you are saying is unless I choose to re-finance the house with a new loan. They will not easily be removed?

Also what about the money I used to buy this house? Would I need to come up with a new down payment if I choose to re-finance?

No, If you refinance you can use the equity you have in the house.

When you say "both" I count 4 people; you your wife, your father-in-law and your mother-in-law, is that correct? All four of you are on the deed?

No, My name and her fathers name are the only names on title

Ok, then you are co-owners. To remove his name, he will have "sell" his interest in the property to you. And you will need to refinance the mortgage.