Property

Hi 

My Grandfather had 3 daughters and a son. My Aunty who is the youngest of all, had got the thumb impression of my grandfather when he was sick before death.

Can my mother or elder daughter of my grandfather claim the property or file a case against this?

I know that if it is given as a gift/will others cannot claim - but we feel the way they got the property is illegal. How should we proceed here -Please advise

Regards

Anita