1) it was your grand father self acquired property . he died in 1979 . on his death your father had 1/7th interest in property . ( 4 sons , 2 daughters , wife all are legal heirs)
you have not mentioned whether your grand father left a will or not . i presume he died intestate . . on your grand mother death her 1/7th share will devolve among her 6 children .
2)the family settlement entered into does not mention about share of 2 daughters . although your father brothers have signed relinquishment deeds and received share of money his sisters have not signed any such deed
3)your cousin brother legal notice is devoid of any merits . it was self acquired property of grand father . his son ie your father brother had signed relinquishment deed . cousin cannot claim any share