Partition

Dear Friends,

I need your help regarding a property issue, please answer

whether we can claim on property with following details:

1. Father is mentally retarded.

2. Mother has given a GPA to his husbands brother to deal with property if any on her father in law's property?

3.Mother has expired last month?  (so the GPA is not at all valid).

4.whether sons of the mentally retarded father can claim property of his grand father and there is no will of grand father?