Sale of intestate property

All the legal heirs are entitled to a share in the property hence all have to execute the joint sale deed or the others can give power of attorney deed in favour of one person who can execute the registered sale deed on behalf of all others.

The share certificate is not a title document.

The society can directly give NOC for sale of property by the legal heirs.

Yes, you all brother and sisters can give power of attorney to  your mother and authorized her to sell the flat on behalf of you all.

Well advised by experts I concur.

Sale of the flat / property do not require transfer of share in the society but transfer of title which stands in the name of your mother with all siblings.

GPA or SPA given to either of you will suffice to complete sale transaction

Thank you all for your valuable advice.

You are welcome for your appreciations.