Best option to transfer flat to son ( co-mowner) vide gift deed / relinquishment / release deed ?

Am parsi son/ co-owner of flat in suburbs of mumbai. mother first named in deed of assignment which was self acquired by mother in 1986.father expired / elder sister was mentally and physically challenged- now expired recently. have a younger married sister who has on her own wisdom/ judgement boycotted us - not on talking terms with us(family) since (2002)now more than 18+ years .younger sister has never ever supported family morally nor financially for reasons best known to her. maybe stigma of having a mentally and physically challenged elder sister. father in his life time was hospitalized 5-6 times / mother 86 years to-date hospitalized 5-6 times with myself supported single handedly through company mediclaim policy . likewise taken care of elder sister from my own income. now mother on her own insistence / urgent intuition wishes son (myself) co-owner of flat to legally give her share to me. best option to transfer flat to co-owner (myself) without any future complications from younger sister who is a potential trouble maker / problem child. less said the better. - jealousy - revengeful - bad mouthing is second nature. please advice as mother's health deteriorating slowly and surely. nota biene - am a parsi zoroastrian. would also prefer to include my wife' s name in the immediate future because i feel life is uncertain and she be protected to that extent.