I told them I'll take him this week when he asks, or if he says yes when I ask him. I made it clear though that he needs to initiate. Beyond this week I'll only take him if he asks (and hasn't already gone in his pants, like he did this morning).

It's great that he's already aware of when he goes and able to communicate it, and I've been encouraging to the parents on that point. I think they can continue with the "potty prep work" ie: letting him sit on it, reading the books, catching him when they can, but I don't think going straight for training him is going to do any good right now.