I wouldn't make that call myself unless perhaps I had a prior/good relationship with the family I was calling. With that being said, I guess I don't have a major issue with the one additional phone call from the head of the organization, as long as they end the call politely and don't try yet again. An excellent response to the question would be that "we appreciate and are honored by your interest, but we have already committed to this other organization, and I am sure you would agree that once you make a commitment to an organization, that they are counting on you and you should follow-through, and that surely they would expect that from their previous commitments as well".