Actually, I choose neither side, but since I had to make a choice, I am a wife. That said...
Family friends are friends, even after a divorce. They shouldn't be caught in the middle and asked to choose sides in an event that they are not involved with (hopefully, they didn't cause it). Friends are not like who gets to keep the dog or who gets Aunt Lucky's silver set. They are independent of that situation and should not have to choose to be on one side or the other in a fight that is not theirs.
I like the example that Jada Pinkett and Will Smith set, for an example of a couple that a lot of people know. When they got married, Jada was having none of the typical and usual bickering that goes on between couples. She immediately befriended Will's ex-wife, Sherry, because there was, after all, a child involved. They decided, all three of them together, that they were going to set a good example for the kids and not disrupt or mess up anyone's life of make people choose sides because of it. Jada and Will have one of Hollywood's longest-standing and "least" troubled marriages, though they've had their ins and outs and ups and downs.
That example, even if something happened and they ended up divorced (God forbid) was one that everyone can use.
The question then becomes, how intimately connected are the particular friends with the husband or wife and will they actually "take sides," as some tend to do. It's left up to the family friends who actually gets 'custody' of them, if there is any to be had.
The next question is, were there any rights or wronged in the relationship, or did the couple just part ways because of the old tag line, "irreconcilable differences." There is a natural course that these friendships will take based on who the friends felt closer to, so sometimes the decision is already made and the die cast before the final papers hit the mailbox.
Another popular example that I can think of happened in the movie "The Runaway Bride" with Richard Gere and the actress who played his ex-wife and the ex-wife's current lover. They didn't choose, the man in the middle (the ex-wife's new boyfriend who was apparently more loving and attentive) stayed on as a friend to both of them. (I was actually tickled about the way the movie's writers crossed some wires with Gere and Roberts from Pretty Woman, but that's off the topic).
Joint custody of friends is always the best answer, but not always the most feasible one. It really depends on the situation and who and what is involved.