Property Issues

Hello Sir,I am Lakshmi.I am here to ask about my dad's property.My dad and mom were in joint family for 14 years after marriage and he got married at 19 years(1990) and after that they divided.During division we didn't get any sort of financial support from my Grandparents.Its been 12 years since we(dad and mom) divided and till we didn't get any property division.My grandpa says its his own property and my dad didn't do anything.My dad is first son to my Grandparents and he have four siblings,in that four siblings first brother is missed from past 26 years and two sisters are married very long back and second brother have two daughters.My dad have son and daughter.My family is tortured in all possible ways and harassed and not giving the share what my dad earned during joint family.My dad's sister demanding for equal shares.Can you please suggest under what act my dad or my brother can apply for there property and How to make my dad to get his earned property.My brother is 25 yrs and myself 23 yrs.