Relinquishment deed

From your query it appears you do not have either a transfer deed or a relinquishment deed on the basis of which Dev Authority will accept your exclusive ownership over the immovable property.You have not stated who are all successors in interest of your father dying intestate. If property is leasehold having limited right or freehold having heritable and transferable rights. Whether fathers property have been partitioned under local law of Maharastra, if any. Better you consult a local lawyer with these details. 

There are uniform prescribed formats for every transaction and depending on the transfer/mutation, relevant documents required for such specific purpose should be enclosed.  A relinquishment deed from other legal heirs of the father or succession certificate is required for mutation purposes.

The information provided by you is incomplete. If your colleague's father died intestate and nominated your friend then as per the latest amendments made to the Maharashtra Cooperative Societies Act,  vide Section 154B (11) your friend will be registered by the Society as Provisional Member and he will be required to produce testamentary documents such as will or heirship certificate or succession certificate or deed of family arrangement made between all the heirs of the deceased person to make him a full-fledged member of the Society. Until then the share certificate will describe your fiend as Provisional Member with limited right of attending GB meetings and vote . 

Is your friend the only legal heir to his late father?

No,

Alomg with him there are two sisters.but he got the NOC from them and his mother as well/

NOC is not legally valid in the case of immovable properties, a proper relinquishment deed duly signed and registered by all co-sharers (two sisters) can only get such title in the name of the claimant.

Like to inform you that his deceased father has made a will mentioning his mother and him as a legall nominee for the said flat

Genelotgical Family Tree of surviving members after death of person, issued by Revenue Offifer followed by legal heirs and surviving family members certificate of Revenue officer with supporting affidivits and also relquinshing deed registered before Sub Register is what you have to produce or go by nominations as suggested by expert above

R.S.K.Singh

Then mother relinquishing her share is a mandatory requirement.  Please go through one-sentence guidance to avoid too many posts and replies.  Relinquishment through deed and registration is mandatory, as the will states mother and son.  NOC is not valid for relinquishing share in immovable property.

Yes, you cannot be the absolute holder of the property unless the other co-owners relinquish their rights and interests through a registered deed.

Let your colleague may consult a local prudent lawyer with all relevant facts of the case where you have neither any locus standie nor complete information.