You can try checking with the State Bar or here, for pro bono lawyers: https://www.google.com/search?q=new%20york%20pro%20bono%20probate%20lawyers&ie=utf-8&oe=utf-8
You are right to handle this through a lawyer. It can be very confusing and much more expensive in the long run, to try to do this on your own.
Good luck to you!
*** LEGAL DISCLAIMER I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in your state. The law changes frequently and varies from state to state. If I refer to your state's laws, you should not rely on what I say; I just did a quick Internet search and found something that looked relevant that I hoped you would find helpful. You should verify and confirm any information provided with an attorney licensed in your state.
In New York, a will that is not witnessed is no will at all. When there is no will, the court has procedures for intestate administration. For a substantial estate, many lawyers will defer their fee and take it from the estate assets. The size of the fee is usually based on the amount of work involved. If the estate is very small, there are small estate procedures that are inexpensive and do not require a lawyer. The clerk of your local Surrogate's Court can answer questions about such proceedings. It's better to go in person than try to get such information over the phone. If you go there, the clerk will usually give you the necessary papers and explain what information is needed.
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You'll need a lawyer to take a look at the Will and see if it meets the formalities of execution to be valid. Some local Bar Associations and law school clinical programs have events (sometimes monthly) where you can go in and have a document reviewed pro bono. You might check those in or near your county. It's worth calling to find out.
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