In a certain society, there are two marriage groups, Red and Brown. No…

In a certain society, there are two marriage groups, Red and Brown.

No marriage is permitted within a group.
On marriage, males become part of their wife's group; women remain in their own group.
Children belong to the same group as their parents.
Widowers and divorced males revert to the group of their birth.
Marriage to more than one person at the same time and marriage to a direct descendant are forbidden.

A Brown female could have had:
i. a grandfather born Brown
ii. a grandfather born Red
iii. two grandfathers born Brown