Grandchild lives full-time with grandparents who have legal joint custody with the dad. The mother is long gone.

Grandparents don't need the exemption for the grandchild. Dad would like to claim his child as dependent but that can't happen unless the grandparents can waive the dependent via Form 8332.

So, the question is can a grandparent, who has joint custody with the dad (their son) of a child, waive the dependent exemption and confer it to the dad using Form 8332?