Wa`alaykum as-salam wa rahmatullahi wa barakatuh.

 

Your uncle is committing a grave sin by denying the rights of legal heirs to your grandfather’s estate.

You should seek the help of a knowledgeable Imam or scholar or wise person in the community to speak to him so that he comes to senses and distribute the property according to the Islamic rules of inheritance.

If he still refusing to do that, then you have the right to resort to legal measures.