You can contact and attorney and try to open an intestate (without a will) estate. But, your aunt (his daughter) may also try to open an estate (or object to your petition to open an estate). She would most likely have priority to be appointed executrix or personal representative since she is his daughter. It would help if your mother petitioned to have you appointed - or at least she could sign a document stating it is her wish to have you appointed. Your mother is entitled to her share and I commend you for assisting her. Please contact an estate administration attorney in the jurisdiction where your grandfather died. That is the proper venue for his probate estate.
I'm sorry for your circumstances. To answer your question, yes, you need an experienced estate lawyer in the jurisdiction where your grandmother died. The attorney can review the titling of the assets and make sure your mother's interests are represented. Good luck to you.
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Assuming that your grandfather lived in Nevada, probate needs to occur here in Nevada.
If there is no will, the surviving child, if up to the task, is the most likely administrator of the estate.
In the absence of a will, his estate would be split between his children.
If he died in another state, you need an attorney there. Nevada's law on this is a "typical" law, but states vary, an only an attorney licensed in the appropriate state can give you advice.
If there is no will, and if none of the properties or accounts were previously titled jointly with either your mother or your aunt, all of your grandfather's assets would pass equally to the two of them. It is not possible for you aunt to have title pass just to her without a probate or a Set Aside, depending on the value. Your mother would receive notice. Alternatively, your mother can petition to Probate or Set Aside. If your mother is unable, I suggest that you set up a consultation with a probate attorney to gather some information to take back to your mom. If your mom is able to participate by phone, that would certainly work. You are welcome to call my office for a consultation.