Division of ancestral properties

My father has 2 brothers and 4 sisters. My gradparents passed away however when My grandmother died, before there was commercial portperty was distributed among three brothers (on a normal paper). My grandmother had 2 properties under her name as per the letter and was staying with us. She has gone through many medical difficulties however we did not get help from either of the siblings ,hence my father had lost all his savings and investment. due to this one of his commercial property we have to sell. Now one of the sibling is demanding for a part from her share. Also, one of the shop which was under her name, he took it forcefully when my grandmother was alive to work and got the registeration done after her death. Can't we retaliate in this case as My father is the one who had suffered and finished his all savings, investments and even his own share coz of the mother sickness when no one else came forward to help.