To be belts and braces, I would email and phone (I know it seems a bit much but DLP can be a bit remiss on their comms!).
Tbh you should have no problem getting a kingsize bed - there aren't many, but most people have 3+ in a room so need 2 doubles.
We have been with my parents a few times and had interconnecting rooms (so that they could watch the children at night while we went to the bar for a cocktail!). And it seems to be that our room always had the double beds and their room had the kingsize bed. Their room was always slightly smaller though as tend to be a on a corner but you could still swing a cat comfortably!