There are some great suggestions there for you. I would second the Titanic Belfast for teenagers, there is plenty there to keep them interested for an afternoon. If they are into the outdoors, you could make an overnight in Carlingford, it's on the coast, about half way between Dublin and Belfast. There are a choice of adventure centres and water sport activities there. https://carlingfordadventure.com/
I would also recommend the Sky Walk and the tour of Croke Park, the home of Gaelic games in Ireland, it's an 80,000 seat stadium quite near to the city centre. Depending on time of year, it may be possible to get tickets if there are matches on there too. Gaelic Football (ladies and mens), Hurling and Camogie are all played at the stadium.
I am also going to throw in Loftus Hall on the Hook Peninsula in Wexford, it's an old stately home that is a haunted house - it's very authentic, no special effects, a lot is left to the storytellers and the imagination. It's very spooky and a great visit for teens, well really for anyone but I know my smaller kids maybe a little too scared by the stories.
Depending on their interests, I'm sure there will be plenty to occupy your teens throughout the country.