I would start with Freedom class.
I'm worried some of the RCI boats might feel more like shopping malls
Disney ships have shopping malls on them too. They just look a little different.
If you want a different line and you really don't want smoke indoors, Celebrity has a casino and does NOT allow smoking in it. It's next on our mental list. DH likes to gamble a little bit but he truly can't come back in the room in those clothes or I'll go into asthma; since cruiselines frown on people walking around naked, that means DH can't do something he likes.
Not sure what the teen clubs are like on DCL, but on Royal from watching from afar, they seem more like a place to meet up with like-minded kids and go do fun things with them. So your 16 year old might actually like that; s/he could go the first night, feel like s/he belongs (it's so hard to get rid of the "I don't belong" perception if you don't go the first night), see if there are any other kids there that seem to be like him/her, and maybe have others to hang out with. The trouble is the 18 year old, since that's adult age, I'm not sure the teen club allows someone who is 18.
Don't stop your research there, though. Check it out; see if I'm right or wrong.
Cruisecritic is amazing for Royal. Things get touchy over there; ignore it. Take in the info. There's a ton over there.
Ice skating at sea is like nothing else. We saw the ice show the first or second night and wondered why these Olympic class athletes were bobbling. Then a day or so later we tried it. Wow is it challenging! Really changes your perspective on how amazing the athletes in the ice show are.
Movies at the pool are noisy and overwhelming, I'm not going to lie. If you want to hang out there, go earlier and perhaps bring ear plugs. They do have silly things like "sexiest leg" contests (generally won by a hairy man) and even belly flop contests. (poor DH should have won but went in awkardly and had almost no splash given his size...sigh...people were so disappointed) Avoid if you would hate those things.
But they have trivia and things going on. I'd head to cruisecritic and read some trip reports of the Freedom class.
Or before that, go to the Royal site and just look through the info on the Freedom class. Check out wiki to see the relative size of Dream/Fantasy and the various Freedom class ships. Look at rooms, etc.
Many people put kids in an inside cabin and adults in the other ones.
People like the inward facing rooms because it's what they can afford, or they get seasick looking at the ocean, or fear, or interest in people watching, etc. My cousins went on Royal (a smaller ship) and got a promenade-facing room, and loved it. They are going on an even smaller ship sometime soon and I'm sure they'll love that, too. I'd love to get the Ben&Jerry Sweet (on the ships with a promenade) but it only sleeps 2 and we're a family of 3. It's over the cow that's over the Ben&Jerry place (that used to be the not-really-an-exception to the rule of "the only thing you pay for on Royal that you don't pay for on Disney is soda", except that Disney had nothing like it...but now Disney has Vanellope's, which is such an obvious copy of Royal having a premium extra-pay ice cream place it's not even funny) and it comes with free B&J ice cream. I think it's actually treated like a junior suite, too, which means double cruise points.
Hey, maybe that would be a way to focus your plans? Seek out a cruise where that room is available; put the parents in the "sweet" and the kids across the hall?
We've so far been in interesting rooms. That's how I've chosen ships/rooms/sailings. On Radiance we got a "guarantee" room, so they chose the room for us. We were in 7100 which is an oceanview over the bow (by the way, on Royal you can go onto the helicopter pad at the bow, unlike on Disney ships). Neat room. On Freedom we've been in 1700 which is deck 10, aft, which a huge balcony. It's got a funky deal with how many you can book in it; I think it's 3 exactly, no more no less...though. We were most recently in 1864, which is a new panoramic oceanview, plunked down at the front where the jogging track used to go to (now the track is shorter). Great room. Up next we have 7688 on Adventure, and while it's officially classed as obstructed view, it's an AMAZING balcony.
Not sure what I'll book after that! That "sweet" is looking better and better, though I'd have to leave hubby or son behind or get a second room for it. When you're lost, though, finding one thing to plan around can be helpful, and that way helps me.