It's been a long time since I've seen the movie, so I don't remember if they stated it was the parents' agreement or not. I agree completely that it's an asinine way of doing a custody arrangement, but sometimes it's not up to the lawyers/judges. If the divorcing couple agree on the terms of a divorce, the judge basically just confirms it as an order. The lawyers are to represent the wishes of their clients, sometimes regardless of how ridiculous they're being.

Actually, David Tutera (a minor reality TV host) and his ex-husband are doing this with their twins (although I'm assuming they'll actually know the other exists). There is the added wrinkle that each man is keeping the child with his own DNA - they'd split by the time the surrogate gave birth. But it caused some ripples when they announced it, since everyone pretty much agrees that it's ridiculous. Even Tutera's ex, honestly, from what the interviews sound like. It's just a sad situation.