Is "tanzil" (representation) permissible in inheritance, and are grandchildren entitled to their father's share if he dies before their grandfather?

It is permissible for a grandfather to bequeath to his grandchildren who are disinherited from inheritance an amount equivalent to their father's share had he been alive. This falls under the category of a will, provided that the bequest does not exceed one-third of the estate. If it exceeds that, the excess portion is subject to the approval of the heirs. As for a son who dies before his father, he does not inherit, nor do his children inherit from their grandfather if a direct son is still alive.