Please advise very urgent

Hi every one....

My father apply a dda flat on his father name.On this flat we are living from last 30 years.All the installment on the flats done by my father and all the construction was made by my father  and all the dda documents we have.

Now seen is that my grandfather have 9 childrens and they want to share on it.

please advise is there any rights on it if yes so how much share on it.

Thanks