Can provisional member of a jointly owned property sell that property

There is a shop in our housing society which is jointly owned by Sister & brother. Sister name is first in agreement as well as in Share certificate. The brother died intestate & had nominated his son for his share & interest in property. The Son of deceased member informed the society that his mother (wife of deceased member) is missing for more than 26 years but Missing complain lodged in police station is of 04/12/2021.To gain regular membership, society had informed the son to submit Legal Heir cert or succession cert or registered family arrangement but he denied to do so. Registrar had order the society to admit him as a member on duly nomination basis. The society had then accepted him as a provisional member on the basis of nomination. But recently he(provisional Member) & his Aunty (Primary owner) had sold the shop to third person through a Registered Sale agreement. The society need to know, what is the status of this third person, will the society have to accept the third person has a member? please guide.