Our DC has ADHD and we went to Efteling last summer. If you go to guest services they will give you a pass to skip the queues. We only used it when the queue was obviously too long for her to wait. Where the queue was quite short we just waited with everyone else.
We got on the rapids ride without queuing at all by using the pass, and also the boats, as the queues were long. We did find that while waiting in the disabled holding area a family with someone in a wheelchair would come along and give us really dirty looks for being in "their" space. The staff were very good though and strictly first come, first served.
Just a tip. If you use the pass on Symbolica they take you into a different waiting area which is inside (my DD hates indoor queues) where you wait for ages, but at least you can sit. They have a dedicated disability car that runs on a different track so you have to wait for that one to come round.
Symbolica is actually 3 different rides, but the disability car only does the green one. Also you need to be in the front seat to be able to press the buttons for the interactive bit, and people with physical disabilities get put in the front. DD was a bit miffed to have to sit with a random grandad!
They offer a "single riders" line to beat the main queue and it was clear that people were getting on in 2s and 3s from that line because they use them to fill up the cars. That may be a way to do the red and blue rides without having to queue too long.
I don't know about carer discount because we went as part of a package and stayed in the hotel. We had a fabulous break. Enjoy!