@GraceUnderPresure
Weymouth!
(Plus you can take the scenic open top bus or drive to Portland Bill lighthouse, to West Bay/Bridport or to Swanage (stopping at Lulworth Cove, Wareham and villages- although it takes 2 hours!)
Weymouth also has the harbour with many pubs, cafes and restaurants in addition to those on the Esplanade. They might want to have a go at crabbing?
Your teens may enjoy a fast boat ride on a rib to Durdle Door - it’s great fun! (They did fast donuts 🍩 when we went on it!)
They might also enjoy Bowleaze Cove which has open air movies/sports on a big screen, adjacent to a snack bar (hot dogs/burgers/pizzas) and indoor restaurant for meals, arcade, air hockey etc (it’s open to all but part of the Waterside holiday company).
Also just on the causeway to Portland is Billy Winters which is a cool beachside diner, sometimes with a band playing and you can paddle board there.
(There is also a fabulous new Malaysian restaurant with very reasonable prices called Malaya Lah in the Carlton Hotel on the Esplanade with sea views. The White Pepper restaurant is very good too: coastal Keralan Indian cuisine).
I’ve never been there but friends highly recommend the Tank Museum at Bovington which is interactive.
I can’t help regarding accommodation but there is a Dorset agency for holiday cottages in the county:
www.dream-cottages.co.uk and probably other agencies such as Sykes.
Swanage is also a lovely place but smaller so not so much to do for young teens.