Mother property (self earned) 50% gift deed made on son's name

Property in the name of my mother, After long battle, my mother agreed to make gift deed (registered in 2012) of Ground & First Floor and remains IInd & IIIrd floor retained in her name only. We are four father, mother, sister (married 2011) and son (my self). My put my efforts to build the house on my mother's land (property registered on her name) after completing construction she started to say 50% yours and 50% will be given to my sister. I got married in 2005 and I have invested my spouse money into the construction for future betterment. From the day one my mother started to fight with me and my wife and I have attempted for suicide also. Finally with mediators she agreed to make gift deed for 50% (Ground + Ist Floor) and she retained IInd & IIIrd floor. Father age 68 and mother's 58 years. They are staying in IInd floor and we are not interacting with them stopped to talk completely. Around 4 to 5 years back, In front of the family members my sister agreed to take 5 L and she won't claim property. Somehow later she refused the offer. Now my mother proposed to give 5 L so that they can transfer IInd & IIIrd floor in my name. My worry is tomorrow my sister proceed with legally to claim? what kind of document should we go? will once again gift deed will work? Pl suggest documentation part. regards Srinivas