Daughter's right in ancestral property

My Grandfather (still alive) has 2 daughters (my mon eldest of all) & 2 sons. Grandfather received ancestral property land after my great grandfather died in 1965.Latest In Jan2015 2 sons have gone ahead registered land property (equal divided between themself ) into their name without any concent/permission and refuse to share the property with sisters (mom,younger sister).Grandfather is not supporting daughters for their share.We need your advice:1.do my mom have equal share in ancestral property land ? .2.What legal actions,next steps to be done to have our share?.Looking for your support.