Legal notice to class 1 legal hires

Hi Sir/Madam, In 2001 my grand father died without a will leaving behind his wife and 5 children(3 male 2 female ), in Oct 2005 my grandmom gift registered half of undivided share to my mother keeping all in witness except 1 female which their family said in word we dont require anything,in 2005 my father constructed 1 floor also. and in 2011 my grand mother made a will to my 1st uncle. Now my mother and my 1st uncle are planning to sell the property, and my buyer asking a release deed, now my big mom son is not allowing to send his mom for sign on release deed, 1 one 3 uncle is missing since 6 year. also during my grand father days he has made properties to all of them except my mom and 1st uncle(but nowhere its written). Now can imy mother send a legal notice to others to settle the matter in front of a advocate? so if no once turnsup in given time, will it be enough for selling property?