You will need the will and a copy of her death certificate at a minimum. I suggest you retain an attorney to file a probate petition in surrogates court. Once letters testamentary are issued the executor of your grandmothers estate will than have the power to transfer title to you via an executors deed.
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Assuming your grandmother left the house to you and your mother in her Will, whomever is named as the executor in the Will needs to file a probate petition in the surrogate's court. Depending on the wording in your grandmother's Will, you may own the house outright or own only half with your siblings owning the other half. You (or whomever is the named executor) should consult with an attorney who does estate administration. My firm handles such matters. Good luck to you.
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