Unless your teens want to sleep in same bed, you have 172, 176, 182, basically the same sleeping setup for each, you have 2 bunks, then dinette converts to bed. We tend/try to just keep the dinette setup as a bed unless the weather is bad, just less work to keep switching it around (kids not eating in camper is also nice bonus)
172 - biggest bunks, but least room as no slide out
176 - you get a slide out so more "hallway" space, but you lose some bunk width
182g - take a 176, flip the bunk with dinette, stick the garage on the back
as already mentioned, I'm not sure how teens would like the smaller bunks of the 176/182. I'd highly recommend going to see a dealer and looking at least at a 172 and 176. The 182 seems about the same inside as 176, just a garage on back. It's kind of a tradeoff of small bunks for a bit more hallway space.. hard to make a call there as 172 is pretty tight on the interior with just 2 adults. The other aspect is cost, as with anything more options means more cost.
For reference/opinion, i have a 172 and 2 small kids. The biggest challenge we run into is storage space, particularly for a longer trip, we tend to use about 1/3 of each bunk for clothes. That works when kids are little, teens would probably be more a challenge. We added numerous storage hanging pocket things, hooks, etc, but still have a hard time between the clothes/food. Though you do get better and more efficient each trip .