Your question implies your mother is living. My answer presumes this to be the case.
Your mother co-owned the real estate in one of two ways. Either as a tenant in common, or by the entireties (joint tenant). if she was a tenant in common with your father, then she owns 1/2, and the estate owns half. If she was a joint tenant, she owns it 100%, as of the date of death.
You should have the deed with both your parents names on it reviewed by an attorney.
The omission to list you as interested person that you mentioned occurred in a conservatorship. That is not a decedent's probate estate. Without more facts, it can't be determined whether you have any claim against her as conservator. Conservatorship cases generally close upon the death of the protected person.
You should obtain copies of the conservatorship court file and review them with an attorney.
This answer is not specific legal advise. No attorney client relationship has been established. It is general commentary on the question presented, without the benefit of a full disclosure of all relevant facts. Seek an in-person consultation with a licensed professional.
I am a NY attorney and am unfamiliar with your state's laws, but I can give you some general guidance. First, it is uncelar whether your father had a will. But, regardless of whether he had a will, you and your sister, since you are both distributees of the estate, would be required to be notified of a probate or administration proceeding.
Just because your mother's name is on the deed, that by itself does not make her the true owner. There may have been steps involved in the divorce proceeding that disposed of her interest in the real property.
If I were you, I would promptly make an appointment with a lawyer who has substantial experience with estates in your jurisdiction.
Good luck to you.
Michael S. Haber is a New York attorney. As such, his responses to posted inquiries, such as the one above, are limited to his understanding of law in the jurisdiction in which he practices and not to any other jurisdiction. In addition, no response to any posted inquiry should be deemed to constitute legal advice, nor to constitute the existence of an attorney/client or other contractual or fiduciary relationship, inasmuch as legal advice can only be provided in circumstances in which the attorney is able to ask questions of the person seeking legal advice and to thus gather appropriate information.
Quite a few issues going on here, title on the deed would control unless a court rules otherwise for some reason. I would hire an attorney if the value of the estate is worth it and get involved in the probate estate.
Your Question is too complicated to answer in this limited forum. The title of the property is important as are the terms of any divorce judgment or settlement. I believe. you need to meet with a probate lawyer to discuss this further. Best of luck to you!