Issue of share certificate to unauthourised flat owners

There are two illegal flat owner who is demanding to issue a share certificate. One is registered Agreement for sale duly registered and another Agreement of sale Unregistered just paid stamp duty in Amnesty Scheme. They are in physical possession of the flat since last 30 years. And paying regular maintenance and other charges. But society did not issued the share certificate and both of them not aware that they do not have share certificate since 28 years. Now the they requested the society to issue the share certificate. The society informed them that your flats does not as per BMC approved plan neither it exits in BMC final approved plan. They further requested that we are staying here since 30 days, paying maintenance and attending meetings, this matter came to light just 2 years back. They further assured that they will give Indemnity Bond duly registered in which they will take all responsibilities of all, if incase any action taken from BMC and if declared as illegal they will do regularisation the said flats at own cost. The society will not responsible for any consequences either in defect in title of the said flat or regularisation, or any action taken from any dept. They will completely responsible, further they assured in written they will not file any suit/petition/complaints against the society regarding illegal flats. Further assured in written the issue of share of the share certificate does not means our flat get regularised, they will follow the proper procedures at their own cost