Rights of legal heirs - GIFTED settlement

Hello, i think you have wrongly mention that your  "father"  gifted all his property. It should be your  "Grandfather".

1.Please mention in which state you residing and when (year) your mother got married. 

2.Yes your grandmother was the class I heir of her deceased son if he was not married and died intestate. 

//My father gifted all his property to his sons, both the self-acquired and ancestral ones he got from his brothers will.//

As far self acquired property, your father has absolute right.

The property he got from his brother's would also be treated as self acquired property and it cannot be treated as ancestral property.

Your mother cannot now claim/get any share in her father's property, that too after so long years. 

yes, i wrongly wrote - its my grandfather, i am at coimbatore, tamil nadu. my mother got married in 1987.

No, all the brothers were married and they have children. One of the them is dead and some say that my granny can ask a part of his share as his legal heir.

what if for the ancestral property? others?

1 I feel that your mother cannot get any share in the property.

2 your grand mother can get a share only if your died-uncle dosen't   have any children or wife living now, and he should have died without any "will" written  by him.

From the facts given by you, your grand father had three kinds of properties: (1) his self acquired property; (2) property willedd by his brother to him and (3) ancestral property.

As far as property (1) and (2) are concerned, your grand father has absolute right to do whatever he wants to do with it.  In that sense, if he had gifted the entire thing to your uncles, your mother cannot complain about it.

Now coming to property (3) i.e. ancestral. 

In the ancestral property, since your grand father died long back (i.e. prior to 1.1.2005), only the male members will have equal share in it - meaning thereby that your grand father and his sons alone are entitled for equal share in the same and your mother has no share.

Your grandfather's share would be with your granny during her life time.  Thereafter, it would devolve on the sons.

Your granny cannot gift her share to anybody.

You say that one of the Sons is dead.  Obviously he cannot be your father.  Therefore you cannot be his heirs. (So to say that your grandma would fight for you as legal heirs of the deceased son is not correct).