I was forced to do something similar on our first DVC stay (3 resorts in 4 nights). moving around and being homeless gets pretty tiring...so just try to adjust everyone's expectations going in. Keep in mind you'll have to be out of your room by 11 am and can't officially check-in until 4:00 pm.
As far as things to do -- they could ride the skyliner and check out different resorts while at BCV.
Depending on what your plans are for the next year -- you could consider getting a water park AP if you think you'll use it for more than 2 days.
There are two putt putt courses by Blizzard beach and two by Swan/Dolphin (which you could walk to from BCV).
Other activities could include renting a boat for an hour and just messing around (boats are actually a lot cheaper than I would've thought). Doing this while at BLT/Poly would be a good option. Could also just ride the monorail around...or take a boat to fort wilderness and rent a golf cart and drive around that area.
Maybe do some sort of disney resort scavenger hunt?
https://herewiththeears.com/free-sc...-do-at-some-of-the-walt-disney-world-resorts/
I've never done any of the community hall stuff at the resorts -- so I can't really comment on the free activities of each resort and whether they'd be age appropriate for teenagers.
Other than that -- pool time would be the main thing I would suggest.