Wow, summer time is super expensive! We paid 1300 pounds for 4 nights in DLH during october half term!
I would check if you are able to change the room to a standard one in the lodges - the default setting is for montana rooms and this will effect the price.
It may also be worth pricing up just one adult and getting an Fantasy annual pass for the other one. Bought with a good deal, the passes can be had for around 130 pounds. sometimes the cheaper cost of the room with only 1 adult more then pays for the cost of the pass. You then also have the added benefit of 20% discount in most of the shops and 10% discount on food and drinks.
Definatley price up eurostar seperatly - i think prices start at around 69 euro return when booked early enough - you can phone them and they should be able to let you know when tickets for your dates will be released.
Also worth mentioning that promoparcs also have a special offer on Annual Passes at the moment, and both them and CE Multivantages had the same offer before and during the summer. For each adult pass, you can buy a childs one for 35 euro!
At the moment it costs euro 168 for 1 adult and 1 childs fantasy pass - about 134 pound - worth also pricing up the trip for just one adult and the free child. You can add the other too onto the bbooking room only for just the tourist tax of around 1.20 per night.
Sometimes it is worth playing around with the figures..........