Solution for distribution of property safely?

My grandfather G has 2 sons A and B, there are 3 flats in issue, G has a 2bhk flat 1, A also has 2bhk flat 2 and B has a 1bhk flat 3 , all in there name. But B doesn't live in flat 3, he lives somewhere else and G lives in flat 3 because it is on lower floor. Now B sends legal papers claiming that he has shares in each and every flats as he also paid some amount in buying all those flats (even though he didn't). But after some mediating B want 2bhk flat 1 as his own and told G to take 1bhk flat 3 as their own in name and exclude A from having any share flat 3 from getting it after G's death. My grandfather G decided to accept the request of transferring his flat 1 to B and B's flat 3 to him. But angered by this B's decision, what are G's options left further like:- 1) can G in his will left his everything to his only grandchild, to avoid further distribution to his property? 2) how can G transfer his left property to A without B claiming to it after G's death? etc