A power of attorney is a document that gives another person power to act for the signor. However, the easiest way to avoid receiving money and property from the estate of your father and give it to your mother was to execute a "disclaimer". A disclaimer is a document that waives the signor's right to property received from an estate, in this case, your father's.
The rights afforded under the powers of attorney that you and your siblings signed to the attorney in fact (your mother) depend on the language in the documents. If the powers of attorney encompassed the power to execute a disclaimer, and if your mother used that power to execute the disclaimers, then you may have waived your rights.
There are several exceptions to the general rules that a power of attorney is valid. If you were children when you signed the powers of attorney, there are complicated rules involving fiduciary duties and rights under intestacy law (how property passes without a will) and these are very state specific. I would recommend seeking the advice of an attorney before moving forward.
The right to receive money under a will or trust normally is not a vested right, which means that your mother could change the documents at any time before her death. She also has the right to use the proceeds of the house as she wishes. The only way to challenge this is to challenge the original signing of the powers of attorney or other documents and challenge the transfer of the house. Please carefully consider your options with an attorney if you want to go this route. Family estate law suits can be complicated and may have unintended consequences including jeopardizing your family relationships and eating away the majority of the estate.
This situation shows the need for an estate plan including a will, a trust, powers of attorney, and health care directives. If these documents had been in order, this complicated situation would not have arisen.
It is very difficult to answer your inquiry. What you do need is a probate attorney. However, it is very hard to understand how your mother had a claim on the house and why she wanted to protect herself from her own children. You do not tell us if your parents owned the house jointly or if it was only in your father's name. Assuming it was only in your father's name, and that your parents were not married, and he died without a will, then according to the intestacy laws on NYS, the house would go only to the surviving children. If this is the correct analysis, then what your mother did was to try to disinherit you all. However, a power of attorney does not have the legal authority to determine how the assets of a decedent are given to the survivors. I find it interesting that your mother is now promising to share with you the proceeds of when the house is sold. Given her past history, I have a hard time believing that will happen.
On my profile there are several legal guides. I recommend reviewing the following which may be helpful to you:
Hiring a lawyer helpful; Is it Legal? Is it Illegal?
Understanding the different court systems;
legal terms used in litigation helpful.
Estate Litigation with a will
Estate Litigation without a will
Mr. Sarno is licensed to practice law in NJ and NY. His response here is not legal advice and does not create an attorney/ client relationship. The response is in the form of legal education and is intended to provide general information about the matter in question. Many times the questioner may leave out details which would make the reply unsuitable. Mr. Sarno strongly advises the questioner to confer with an attorney in their own state to acquire more information about this issue.