Transfer of share in housing society

Member had nominated his wife and had three daughters and one son. All are married. Now son approached for the name transfer application of society share after several months on HIS name and had obtained Consent from Mother who is a nominee. He was advised that it can be transferred on his MOTHRES name as she is a registered Nominee. He then said that he has obtained two Property card after his Fathers death. The first card had all legal heirs names while the second one obtained on his name with due legal submission fro all tha sisters and mother WITHDRAWING their rights an SECOND Porpery card mentions this too. His mother is still alive and healthy. Question : Can we transfer shares on his name with the two property cards as eveidence of legal heir ? If yes , then can this be considered as sale ? If yes should we charge transfer fees like other sale ? Do we need to get sale documents if he is ready to pay transfer fees ? Can any family member later sue society ? CHow can we indemnify us ?