By transfering ownership to her new husband your mom may have divested all interest in the house to him if he was to out live her. However without looking at the deed which transferred ownership it is impossible to answer this question. It all depends upon how title was taken. I would suggest you get a copy of the recorded deed either from your mom or the county clerk and discuss this matter with an attorney.
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Most likely if your mom "goes" first the house will go to your step dad. There is a chance that the deed may read differently but doubtful if he has a mortgage on it.
The answer is: it depends. It depends on what the deed says. There are three main types of co-ownership of real property. For husband and wife, generally, when one spouse departs this life, ownership passes to the surviving spouse by operation of law. If your mother and your step-father were married at the time the deed was changed to include your step-father's name, that's probably the case. Now there are other ways that ownership can be vested, so it depends on what the deed says. Definitely consult an attorney about this. You can refer to my website for more thorough information.