Flat transfer

Dear Sir my grandfather purchased a flat in 1973,he made a will in 1986 and died in 1987,as per his will the building transferred flat to my father & my grandmother in 1993, then they both nominated my mother as nominee.. in 2002 my grandmother died, and the building transferred the flat share certificate solely in my father's name, but my father did not make a fresh nomination. now in 2011 by father expired and we applied for transfer of share in my mothers name being the nominee (as per earlier nomination) the building did nothing for one and a half year so we went to registar, and suddenly my nephew (who stays on the same floor) has become greedy and is demanding a share in my flat (after more than 20 yrs) his father who expired in the year 2000 never had any objection. my nephew says how did the building transfer the flat twice and the building has done a wrong thing since my grandfathers will was not probated everyone says that he is creating only nuisance and harassment to a widow pls can you give me your advice thanks