Legal Question in Wills and Trusts in Illinois

Good question. The title and deeds need to be examined carefully. It sounds like your father and mother each owned half as joint "tenants in common" instead of the more common joint tenancy with right of survivorship.

If your father owned 1/2 as tenant in common then his 1/2 of the house would pass through his estate, pursuant to the terms of his Will, if he had one, or if no Will then by state intestacy law. Assuming no Will, then if your dad was unmarried at the time of his death, his estate would pass equally among all his children (including children from a different mother, if any) and to descendants of any deceased children.

In order to be sure I would need to have a look at the deeds. If I understood correctly, it sounds like your mother is no longer an owner of the property. You and your sister would likely have become co-owners with your father when she signed over her rights to you.

If the deed shows that you are joint tenants with your father then you and your sister would be the surviving joint tenants. The normal situation is that the surviving joint tenants are the new owners when one joint tenant dies.

It does not matter that you are a birth child or that she is a step child. What matters is that you were co-owners (joint tenants) with him when he died.

I recommend that you take the deed to an attorney and find out for sure.