Booking three adults in a room with Priceline?

[SL6827]

If you wanted to book a room with Priceline, (not the express type, the normal way) how do you do it with a party of three adults or three adults and a child? It only allows for two peoples names on the reservation form? I am assuming you just can call and add the kids, but I know Disney will charge you for a third adult and how would you go about paying for that?