Hello ! Thank you for reading my question.
If my husband and I own our home as tenants in common, is it possible for him to add others (such as his adult son) to the deed without my knowledge, or would I need to sign off on such a transaction as well?
Thank you .

While of course he could do a quitclaim deed and do it, I do not believe it would hold up in court.

Several factors, first it should require both to sign, and in many states, even when it is not "in commom" the wife has to be notified, under a spousal notification rule.

But if you want to check, you can go to the court house and check the deeds filed.

If you own your home as joint tennants, he can assign his share or interest in the house to another party

If you believe he is doing something wrong, please have a real estate attorney in your area review your deeds and give you advice on your specific state.