1. Well, in support of actual line of descendant many public or private authority insists on Succession certificate as the same testifies on the number of legal heirs a particular person leaves behind.
2.So if the Society asks for the same there is nothing illegality in it.
3. However do note that on death of your mother you, your brother and sister will each inherit her undivided 1/3rd sahre from her 50% share in the proeprty.
4. So on production of the succession certificate the society will issue share certificate in the name of your siblings only and not in the name of your wife.
5. However you can ask for making your wife nominee in respect of the your own 66.66.% share in the flat.