You'll need a local attorney. I've had a similar situation happen to a client in Texas. The surviving spouse was successful against the step-children, but the success was painful. Condolences on the loss of your husband.
There are four elements for a valid joint tenancy with right-of-survivorship: (1)Time - the co-owners must acquire the property at the same time; (2) Title - the co-owners must have the same title to the property; (3)Interest - each co-owner owns an equal share of the property; and (4) Possession - the co-owners must have an equal right to possess the whole property. Assuming all of these elements are satisfied without challenge, and the operative words creating the joint tenancy with right-of-survivorship where used in the granting instrument, you should not have a problem. If you have concerns you should consult a real estate attorney and ask him to review your deed and your specific circumstances.
If your spouse held the property with his first wife as tenants by the entirety, then he became the 100% owner of the property upon her death. He was then free to re-deed the property to you and him as joint tenants.
Because the deed specified a joint tenancy, it passes outside of the will.
I am not a CA attorney, laws vary from state to state, therefore you should always consult a local attorney.
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