Good afternoon Lou Anne,
I'm Doug, and I'm sorry to hear of the confusion. My goal is to provide you with excellent service today.
As no will was made by your mother, then under the law, her heirs would share in the value of any assets remaining in her estate at the time of her passing. Your mother's children would each be entitled to an equal share 1/3 of the assets and particularly the burial plot----when it is sold, the profit from the sale would belong to all children of your mother, in equal shares.
You say that there are two of three sisters remaining. If one of your sister's died----and dies before your mother died,----then your deceased sister's share of the profit would go to her husband if she was married at her death, or to her children (again in equal shares---based on the deceased mother's 1/3 share) is she had any. Otherwise her share would be divided between you and the remaining sister.
So in conclusion, if your sister died before your mother, then your sister's children will legally be entitled to share their mother's 1/3 share of the sale of the plot. But if your mother died before your sister, then your sister's children would not get a share of the profit from the sale of the plot.
You may reply back to me using the Reply link and I will be happy to continue to assist you until I am able to address your concerns, to your satisfaction.
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I wish you and yours the best in 2016,