If my wife is left her fathers house do I become a part owner

Marital property laws differ in various states, but in most states you would not be a part owner just because you're married to the owner.  In New York, for example, inherited property is separate and not part of the marital estate.  That being said, however, the only right to help in the lawsuit which you might have as a part owner but do not because you're not the owner, is the right to act as an attorney in defending the case, which would probably be a bad idea in any case.  You can be a witness (assuming that  you have personal knowledge of any relevant fact), you can help pay your wife's legal fees, you can help investigate the facts, etc.