What are my rights if I live in a house owned outright by my stepfather who just passed away last week?

Unless the home is passed to you via trust or probate court or had a lease there is no right of possession.

The estate will have to be probated for a change in title to occur unless he owned it in joint tenancy with his wife and she is still alive. ?None of can answer your question without knowing how the title definitely was held, is his wife, your mother still alive, etc.