I really like Poly in the summer. Look into booking a cabana for the day at the Oasis pool. It will get you lots of comfortable seating in the shade. The pool is shallow and chill. We use a car service with a grocery stop and pick up snacks, water and drinks so we brought food and drinks from our room in a nearby building, and ordered a lapulapu from the pool bar. You can book half or whole days.
We also liked watching the MK fireworks from the beach. You can monorail to visit CR and GF.
I think BWI is also a good choice. There’s a lot of activity on the Boardwalk that might interest the teens. Y’all could also easily walk over towards Epcot and utilize the skyliners to check it out and even visit the skyliner resorts. I also like the quiet pool at BWI. I imagine both CL’s are fine, and will allow you to bring food down to the pool area as well. We go to parks daily but usually just for 3 hours or less. Resort time is much more relaxing especially when the weather is warm and the parks crowded and crazy. During winter trips we tend to linger a bit longer in the parks to enjoy holiday decorations and events.
Your trip sounds wonderful! Enjoy!