distribution of property.

My grandmother is no more. If my grandfather will be die. Then who will be the legal owner of my grandfather property. If my grandfather have 4 children (2 sons and 2 daughters.all are 18+) one of them is mentally not fine or say children mind with having a 38 year old age. If his daughter claim for share in grandfather property which is earned by himself(grandfather). Or if my grandfather left no bill (vasiyat). Or he can transfer his property to his mentally disturb sons.