We stayed last March in 2 different 1-BR units/views. I also have 2 teenage boys. My older son is the "smaller" one at 5'11" and super thin. He slept great on the under-TV pull down bed. My younger son is over 6', much broader, and flops like a fish when he sleeps so he got the sofa bed. In one unit it was very comfortable and in the other less so, but not enough to complain about.
The living room is a good layout, even with the beds made up, so we still felt like we had plenty of space. The kitchen and dining table help a lot in that area. They appreciated the second entrance to the bathroom off the kitchen area so they didn't have to come through our room.
As far as locations, we had an Island/Garden view for our first 5 nights and I requested a high floor. We were in Room 983 and had a gorgeous view of the ocean to our right and the luau to our left. We weren't as high as we could have been but it was a spectacular view and location. Our last 2 nights we had a Pool view - can't find the room number but we were on the third floor in the same building almost directly across the hall from where we were before (maybe 382?). It was also a great, if very different, view. We were directly across from the volcano which would have been awesome but it was covered in scaffolding, but looking left and right was amazing. However we could not see the ocean from there at all.
As far as tips...they would get their pool bands for the next day every evening so they didn't have to wait in the long lines. They had a great time in the pool, slides, and lazy river but did not love the beach and ocean at the resort. We spent a good chunk of time off-property exploring the island, surfing, and beach hopping. Let me know if you want any recommendations!