The deceased are Muslims
So the Shariat law will apply
From your query it seems that they had 4 children ie 2 sons (your late father and uncle) and 2 daughters (your paternal aunts )
As per Shariat the son takes double the share of the daughter
Thus after your grandparents demise their flat will go to their children in the following ratios:
Son 1 - 33.33%
Son 2 - 33.33%
Daughter 1 - 16.67%
Daughter 2 - 16.67%
After your father's demise his 33% would devolve on you and your sister as follows:
You - 22.22%
Your sister- 11.11%
Now your grandparents had made a nomination in favor of your uncle, yourself and your wife
It is settled law that a nominee only holds the property in trust for the heirs of the deceased member. The nominee does not get any title over the property unless such nominee is also an heir of the deceased
After your grandparents demise, their 4 children were entitled to the flat. One son (your uncle) was a joint nominee with you and your wife.
So all 3 of you were holding the flat IN TRUST for the other heirs of your grandparents (your father and 2 aunts), your uncle doubled up as a joint nominee as well as a co-heir
Just by entering name in the share certificate the title does not get completed.
Ideally an heirship certificate ought to have been obtained for declaring the heirs of the deceased
Now your uncle died. So his 33.33% would go to his heirs. As he was unmarried, his share would devolve on his siblings as per Shariat.
It appears from your query that your father predeceased your uncle
So the uncle's share would go to his 2 sisters. Whether the children of the predeceased brother would get any share from their paternal uncle's estate, I need to check. Will get back.
However please note that after your uncle's demise , an heirship certificate should be obtained for declaration of his heirs, so that the title of the persons to whom the property is transferred ultimately , stands completed and there is no issue in future at the time of selling the flat
Also the view of few committee members that the procedure of devolution of uncle's share to his heirs, is the correct legal view
The view that upon demise of the joint shareholder, the surviving joint shareholders automatically become the exclusive shareholders is not correct.
The flat is held by the parties as tenants in common (co owners) and not as 'joint tenants' (where upon death of any joint tenant, the right survives to the surviving joint tenants). There is a difference between the 2 concepts. In a society , the flat , when held by more than 1 person, is held as tenants in common.