The AP can reserve up to three rooms. I believe that you must show your pass at each check-in. Some CMs will waive that if you show it at your check-in and explain that it is being used for rooms for other family members.
As for info on the Dolphins in Depth, what are you looking for exactly. My DD has done all three experiences at the Living Seas (Dolphins in Depth, Aqua Seas Tour, and Dive Quest). Your AP will get you a 15% discount on these tours. There is an age restriction on the tours (younger participants must be accompanied by an adult) and for Dive Quest you must be a certified scuba diver. All the equipment is provided and you only need to bring a bathing suit. Each participant receives a t-shirt and usually a photo. Dolphins in Depth used to give the participants a video but I am not sure if they do any more. Dive Quest and Aqua Seas, you can buy the video for an extra charge of $35. You will need your park pass, because sometimes they will release the tours back into the park instead of returning to outside the turnstiles of EPCOT. The participant will also need some sort of photo ID. You can book the tours by calling 1-407-WDW-TOURS and they will charge your CC at the time of booking. Make sure that you mention you have an AP so that they can give you the discount. If you have any other questions, feel free to PM me.