Portugal: Lisbon & ? (beach + deep sea fishing)
 

Our family of four (17 yr old twins) have 9 days in Portugal end of July and beginning of August. Flying in/out Lisbon. We planned on spending the first 4 days in Lisbon (maybe a day trip somewhere?). We would like to find another town that can accommodate each kids desires: beautiful beach and deep sea fishing charter. We stayed away from Algarve as we heard sargassum seaweed has impacted the Algarve coast in the past (and we’ve had other beach vacations ruined by it.) Or maybe there has been a beautiful beach down there that has never gotten sargassum (that also has deep sea fishing)? We tried including Azores but it isn't an option. Our past travels that were big hits with both kids were in accommodations that were beach front/near so my daughter could reading a book on the beautiful serene beach and our son had activities to do like deep sea fishing and history. He doesn’t do well with driving around seeing sights, enjoying the scenery or sitting on a beach. I’m afraid the water will also be too cold for him (we’re from Arizona) to go swimming/body surfing. My husband and I are easy to please. We are explorers/adventurers, our kids are not, at least at this age 🙁 Help with a stunning beach accommodation (town or area?) that has deep sea fishing charters too? Maybe a town nearby to explore if my son gets bored.

The best fishing in Portugal is in Peniche ( north of Lisbon) or Sesimbra ( south of Lisbon).
Both towns originated as fishing villages and still retain some of their original charm.
They have restaurants and some accomodation but they don't have the tourist infrastructure of the big cities.
Sesimbra has the edge with a nice beach and nearby National Marine Park.
While it's possible to reach both by public transit, it's cumbersome, a car is definitely a plus.

Peniche tourist site
https://myportugalholiday.com/penich...ism-guide.html

Sesimbra tourist site
https://sintracascaissesimbra.com/se...-portugal.html

Sesimbra fishing charters
https://www.bolhastours.com/en/boat-fishing

@aulop already gave you the fishing spots advice.
But to be at the beach just spending time, I'd suggest Costa da Caparica (downside, ~1h driving time, ?X via public transportation), or you can go to the beaches of the Linha, which basically are beaches in between Lisbon and Cascais. You'll have several to chose from.
As for beach activities, I think they're more focused on Surfing.

The beeches on the Linha, are all covered by train stations so if you guys get bored you can quickly hop on to Lisbon and visit historical sites, the castle, museums...

Thank you for input. We did a lot of research and ended up Doing Lisbon for 3 nights (a day trip to Cascais), 3 nights in Sesimbra (STILL trying to find a deep sea sport fishing charter for bigger fish, not easy!) and a couple days in Sintra. Everyone seems to be accommodated!

Would love to hear how your trip went! What were your favorite places and how did the kids like their chosen activities? Thanks!