dauthers right on mothers property

I have already posted this topic wrongly in family law section and got some important  reply . if some one gave elabarate reply i will be glad.

Sir,

      Please advise me on the following

      My father has property  as flat in his name and as house in my mothers name and he has 2 sons (me and younger brother)and one daughter (my younger sister).   me and my sister are married.My brother is yet to marry.

    all five members are alive as on today( father ,mother ,me ,brother, sister)

   father has given 60% of share from flat in his name to his daughter(my sister) in the form settlement deed and it is registered .( and its present market value compared with toal market value including  flat and  is nearly 40%)

    my brother and me are only left with 30% share each on remaining property in the name of my father and mother.

    Now my sister is asking for the share (1/3)  from my mothers property telling that daughter has right in mothers property.

     But my father and mother refused tellling that they have already given one portion of flat and during marriage they also gifted ornaments.But she threaten legal action against them.

Now

1. Can she claim share in mothers property through court.

2. can the settlement deed be cancelled and total property divided equally between three of us.(note we are not caliming portion given to her as of now , i  want to know if she went  to court then the settlement deed in her favour can be cancelled.)

3. Can she again claim share in my fathers balance property if any will is not made .

Please enlighten me earlier to take defensive action.