When an Associate Member dies she ceases to be such Associate Member. On production of your mother’s death certificate, and an application to remove her name, the Society must act and remove her name within the stipulated or a reasonable period.
No nomination is necessary to make your wife an Associate Member. She has only to apply in the prescribed form (available from the Federation office) supported by your signature.
Either in the MCS Act or in the Model Byelaws, there is nothing to suggest that an Associate Member is a beneficial owner of the flat. Hence removal of the name of an Associate Member is a simple affair.
Adding the name of your wife is a separate independent action, not connected to the removal of your mother’s name.
In olden days transfer of shares and flats were not subject to stamp duty. The parties had only to apply to the society to effect the transfer of the interests. But with the amendment of the Bombay Stamp Act it became necessary to prepare a transfer deed and also to register the same. Once the name comes in the transfer document in my opinion the second transferee cannot be assumed to have no beneficial rights. If so the heirs of the second transferee also can claim rights. Have you got brothers and sisters?
Anyway I do not think that is the reason your Society is not acting. You keep to yourself the above information, you do as I said above and ask for the response of the Society. In the meantime enter your wife’s name as your nominee. The Society cannot refuse it.
If the Society refuses action, make a complaint to the Dy Registrar of your ward.