Property right

As per amendment made in 2005 in Hindu Succession Act it is equal share in property and as of birth right.

We are the 4 legal heirs of my late father. Me(son- married), My mother and 2 Married Elder Sisters. In 1980 my father become the member(Class A membership) of a Co operative Housing society - Mayiladuthurai and nominated me as nominee(i was 3yrs old at that time). Subsequently a plot was alloted to my father in 1982 by cooperative society and he fully paid for the same but plot was not registered(sale deed) in father's name at that time. Suddenly my father passed away in 1984 due to health problems leaving behind without any will.

In 1986 the Co-operative housing society registered the property in favor of my mothers name. She constructed a house by raising the loan from the society at that time and made me and my sisters as Class B members(we are all minors at that time) for surety purpose. Then my sisters got married and subsequently for me too.

In 2009 with my knowledge and with my help, my mother demolished the house and proposed to construct 3 flats there and sold 2 flats  and conveyed 1400 Sq ft (700 sqft for each) undivided share of land to them out of 2600 Sq Ft plot. Now construction work reached the first floor.

Now my 2 elder sisters filed a partition suit claiming 1/4 share in that plot.

My Questions:

What are all the significance / rights / advantage of a nominee of class A member according Tamilnadu Cooperative Housing Society act

I am very much aware that the Nominee doesn't have any advantage normally other than equally sharing with heirs but considering my case since my father mentioned me as nominee at my age of 3 and sudden death of my father can it be considered as WILL