Your grandfather left his estate to your grandmother but his will states that in the event of her death the estate is divided into thirds Can your grandmother then will everything to one person?

yes, if she gets the proceeds of a will, they are all hers. there is some law concening how long she lives, usually if she lives for at least 30 days then it's all hers. she can then do what ever she wants with her money, and it's hers if she inherited it. sorry.