Family trip- like to swim in the sea, hike, bike, eat

Time of year will be a factor along with total amount of time. There are a number of hiking trails depending on where you are, how long you want to walk, and the difficulty of the walk. Maybe take a look at sites like:
https://andaluciahiking.com/hikes-in-malaga/
https://andaluciahiking.com/hikes-in-granada-spain/
https://viasverdes.com/

They will gives you an idea of what’s out there, but there are others. You could also choose to walk a portion of the Camino de Santiago via one of the routes; possibly the Northern route. On it you could also do a combination of bike and hiking.

For lodging, my wife and I prefer Paradors if there is one in the town we’ll be in.

To answer your question directly, there are plenty of locations that suit your needs, but you should do some research to narrow things down. Spain is fairly large with a long coastline and hundreds of beaches.

My first thought is some island hopping in the Canaries—each island is a distinct environment. And hike Mount Teide for sunrise.

Also, the Catalan beach towns north of Barcelona.

I think the Costa Brava in the northeastern corner of Spain will fit the bill nicely, plenty of great costal hikes like the Camino de Ronda and fun in the sun and water in towns like Tossa de Mar.