If you are speaking about two extra adults, you would need to have a room that sleeps 6 booked. If so, I would expect that it could be changed over the phone. Yes, there is a charge for extra adults. We had three 'adults' in our room at the Dolphin once and had to pay an extra person fee.
No, I’m referring to adding the 2 kids. Priceline reservations are only for 2 adults. Wondering if I would have trouble calling and adding 2 kids and if they might charge us more.