Commercialisation of residential apartment

Im staying in a flat in chennai. There are totally 6 flats in my apartment. Out of which one os owner by builder and it unoccupied. In three flats owners occupied and remaining two are rented out to a middleman who inturn leaves the flat as service apartment for nearby hospital. There are lot of practical difficulties and issues related to the ppl stay in service apartment as they smoke , fee patients have contagious disease and lot of chemicals and meds used which creates bad odour . We have two infants and elderly people in the aprtmnt. and issues with maintenance as well since they are concerned abt profit and not abt long term solution or quality and if we raise any question the middleman is abusing us verbally. All three owners staying here are not happy. We raised our concerns to respective owners . One owner in abroad says he cant do anything abt it and other person supporta the middleman and yelling at us nd says its his flat he has all righta to do whatever he wants. Please let us know if this commercialisation is permitted by law. If so what legalisation needs to be done . Because we need to verify from them if not legal we need to ask them vacate. We have not formed any legal association for apartment used to held meeting couple of times and communication over mail group or call. This service apartment is running for last three years