May is my favorite time of year to visit WDW. However, we now have a middle and high schooler who are each taking multiple advanced classes. They can't afford to miss school that not is not for something like illness. I would be comcerned about the end of May due to the end of the school year, finals, review, etc. Will your high schooler be in a spring sport or band where they have a concert? They usually frown on missing games and practices, at least my daughters teams do, and they might lose a starting position. The other thing is if the HS child is in a fall sport, check when practices start. Around here it's The first and second weeks of August depending on the sport. These factors have limited our vacations to June, July and School breaks.
We did two summer trips in a row and, with great planning, they were our best. Rope drop, ADR lunch, hotel for pool/nap, back in the evening if we felt like it was our plan and it worked very well. We have decided to switch it up next year and travel for spring break. We are looking forward to cooler temps.
Good luck in your decision. Things definitely get more complicated the older the kids get.