Like Pamela said the first step is to contact a real estate attorney. You can only sell your mom's share of the house. Your Stepfather's heirs would have to be involved to sell their share of the house. Therefore in short, yes your stepfather's family does need to be involved in order to sell the entire house to a new party.
626 Route 9 South
Freehold, NJ 07728
I understand your difficult situation. In tenancy in common, each owner has an undivided interest in the whole property. Each owner can sell or transfer that interest without the consent of the other co-owners. Tenants in common sometimes donot have equal shares. For example, one could have one-third interest and the other, a two-thirds interest. You should find out how the shares were divided. Upon the death of a tenant in common, that interest passes to his or her heirs or devise's. I highly suggest that you contact a real estate attorney and speak to the heirs as well to make this a collaborative decision. This does not take the place of legal advise. At this time you should contact a Realtor for a market analysis so you know exactly what the home is worth. If I can be of assistance to you, please let me know. I do work in the Lakewood area. I hope this helps you. Best of luck to you and your mother.
Weichert Realtors-Howell Office
Office number: 732-577-0440
Cell number (Best number to reach me): 732-236-8608