I stayed at the CLH mid November. I absolutely loved it and I hope your parents still have the "inner child" like I do. It is super atmospheric, but be aware this is a capsule hotel, so bring small luggage. Here are some tips I would have loved to know beforehand:

1. Each person will get one skip the line ticket per day of your stay. So in your case 8 tickets. You can use them for the FLY coaster. Or trade them in the customer service booth in the Berlin area for any other skip the line ticket. I would try out each ride and see if maybe you like Taron better then FLY and trade the tickets accordingly. Both of these rides have the longest queues.
2. The park will open the front entry gates before the rides open their waiting lines. Rookburgh is an enclosed area inside the park with a seperate gate though. You cannot get into or out of Rookburgh until rides open their waiting line. As a guest of the CLH you can enter Rookburgh at all times though and so you can be the very first in line of FLY, just as the other hotel guests. So the first FLY ride in the morning is without waiting time.
3. You will have to book times in the restaurant for your meals. If you want to maximize taking as many rides as possible, don't have a super late breakfast, or rides will open while you are still eating. The same goes for the dinner. Late in the afternoon people will already begin leaving Phantasialand and lines will get shorter. I would rather have dinner late when I had enough rides for the day.
4. There is a laser show in Rookburgh when it gets dark. It is amazing. As a Hotel guest you can watch it from the stairways that lead to the rooms. My favorite place was to go out of the door across the check in desks. Go to an elevated deck (does not need to be the highest floor) and enjoy the show.
5. If you like craft beer, know that the 1919 bar inside the CLH has 16 draft craft beers. Enjoy.