Claiming my father property

You have not mentioned that how did your father purchased the property from your GM i.e. Gift deed or sale deed, its document No. Dt. In which sub registrar it was registered etc.  Assuming that your father had purchased the property through registered document, then you and your mother are only the legal heirs, your uncle cannot claim the right.

Now coming to the question of your uncle being in possession of the house.  Since your father had voluntarily had given the portion for his stay and you have not demanded him the rents for a long time.  As per law, it is deemed that he has been giving rents to you and you are taking rents, even though he had not paying the rents.  Unless you make the demand in writing preferably through Advocate to your uncle to pay the rents or else vacate the portion, you cannot claim the arrears of rent and eviction.

Atleast now you give him demand notice through Advocate to vacate the portion and if he does not respond to the Notice, file a case before the civil court for eviction, arrears of rent (from the date of demand notice) along with interest, legal expenses.

Thanks for your valuable reply.

A few more details:

In registered document, it's mentioned that my father paid cash to my GM and bought the property. We have power bill, property tax and water bills in my father's name.