I am not exactly sure what you are talking about because I do not have your full history. However, I think that you are saying that the major issue with the estate is that there are missing heirs that are entitled to a share of the estate by law and that since you cannot find them you are having trouble closing the estate.
Unfortunately I must tell you that even though your sister had no contact with her children they are heirs of your mother's estate unless you mother cut them out in a specifically written will. If they are heirs then they must receive their mother's share of the estate before you can close it out. If you have done all your searching and cannot find them then you can request a court receive and hold the assets that are due to the missing heirs. You should know that there is no way that the court is going to let you close the estate without assuring that the missing niece and nephew's shares are either distributed to them or held with the probate court for their later benefit.
I can also tell you that some of the smallest estates that I have cost the most when I have to search for heirs and piece together distributions to children. This is time consuming work.
There is no way that I would call you greedy by not wanting to go through this process. However, this stuff is complex and very specific. Sometimes people do not understand the level of detail and specific requirements that a probate court can require.
I cannot provide you with legal advise. I have provided you with information about the law related to your question. My answer, and any information that you find online, should not take the place of having a consultation with a lawyer in your area to advise you regarding your specific issues.
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