Law /
Poland's Inheritance Law Without Will [21]
Rey115
If you and your brother do not wish to give up your rights to the part ownership of the property, obtain any documents you can. Such as birth and death certificates. Since your uncle was the owner of the property and died before his parents (your grandparents), and he had no children, how much of the property reverted back to the parents and then after their deaths was divided between your aunt and father. Other postings I have read made allusions that if the owner of a property does not have children to inherit the property then the courts would look at the question did the deceased have siblings and/or parents still living and determine how to split the property if I understand it right.
The point here is who owned the property prior to it being registered in your uncle's name. If ownership got transferred while the original owners were still alive to your uncle there must be some kind of court document to substantiate this. By obtaining the certificates of the individuals involved (birth, marriage and death) may also assist in how the ownership got split may help your claims. By obtaining the various certificates will help to prove your claims to prove that the owner was your uncle because the names of the parents would be on all the birth certificates.
Using the certificates and other documents in proper perspective will help. Your best bet would be to locate a lawyer that will hopefully know the real estate laws and inform you if there is a statute of limitations and how that applies to your case.