my ex is forging marrige documents and trying to sell our house

Using forged documents in a real estate transaction could constitute statutory fraud.  Forgery is a crime.  While title companies are pretty good, recent deed fraud cases in Texas show that they are not perfect.  An individual with sufficient knowledge can skirt the usual processes for identifying potentially fraudulent or forged documents in a real estate transaction.  While it is likely that the homeowners will ultimately be able to successfully defeat any attempted sale without their consent, early intervention will likely cost less and result in less time consumed.  The first step is to let the prospective buyer, any real estate agent, and any title company know about the forged marriage documents and that your ex is trying to sell the home without the permission of the homeowners.