The default shares
Spouse, children and parents: 1/4 to the spouse, 1/2 to the children, 1/4 to the parents.
Spouse and children: 1/3 to the spouse, 2/3 to the children.
Spouse and parents: 1/2 each.
Children and parents, no spouse: 2/3 to the children, 1/3 to the parents.
Only one group surviving: they take everything.