You have a number of issues here and they probably involve several different estates. Basically you need to trace the respective estates of each person who had an interest in the property based either on the wills of each person or the laws of intestacy of each person's estate. It may or may not be proper to have the deed end up in "one person's name." You definitely need an attorney to go through the facts in detail because this is too complicated to figure out on the internet forums.
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The best way may be for the surviving niece to bring a quiet-title action, but you most definitely need a lawyer. Do not try this d.i.y. You do not want get the chain of title on this property all screwed up. Find a lawyer in GB who does probate and real estate work.
What should have been done was a termination of joint tenancy by the Aunt and a probate of your Aunt's will. That can still be done, but a quiet title action may be quicker and less expensive.
This is not simple. It is not something for a do it yourself fix; it is not even something for a new attorney. I would recommend William Wolske in Kewaunee as someone to consult.
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As mentioned by others, you have several issues to consider. You should take the deed, Death Certificates for great uncle, great aunt, your parents and the niece, along with Wills if you have them to a real estate or estate planning attorney to figure out the best course of action. The deciding factor will likely involve how the conveyances were created (i.e. joint tenancy, tenants in common, etc.). You definitely do NOT want to attempt this on your own because it may likely result in an even bigger and more expensive fix. Good luck.
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