It's clear that your group likes to travel like I do, spending a good bit of time in each place. Here are a few thoughts:
Sitges: I enjoyed a day-trip there, but you have only 5 really usable days in Barcelona (arrival day will likely be marred by sleep-deprivation and jetlag) and two other proposed day-trips. And you're not going to Girona, which I think everyone would agree is a better destination than Sitges. Barcelona itself is very difficult to see in three days, so I'd not plan Sitges unless you think it would be a fun thing to do (wandering around outdoors in a small coastal town) on the jetlagged arrival day when your brains are fuzzy. That actually might work well. I skipped the Dali House but did enjoy Cadaques. However, it takes quite a bit of time to get there from Barcelona (I saw it while based in Girona), and guide books all seem to prefer the Dali Theatre and Museum in Figueres--for what that's worth. Figueres is a much shorter trip from Barcelona. Both of those Dali sites require you to buy tickets ahead of time, so they are not day-trips you can decide on at the last minute. Also, the train tickets will be a lot more expensive if not purchased in advance.
San Sebastian: Your 5 nights there gives you only 4 days. Santander is one of my least-favorite Spanish cities. It is a perfectly OK place, but it suffered a devastating fire in the 1940s and lacks the historic architecture most of us seek in Europe. I found it comparatively blah. That's the first place I'd cut. I was not a big fan of Pamplona, but I certainly preferred it to Santander. I'd rather use that potential Pamplona day in some other way, however. There's more to the Basque Country than SS and Bilbao (which is larger and has more to see than SS). You might enjoy Hondarribia or Vitoria-Gasteiz, or some of the cute former fishing villages along the coast (Zumaia, Zarautz, Getaria). Vitoria-Gasteiz is on the way from SS to Madrid. You might also use a day to see Burgos, which is on the way to Madrid from both of the Basque cities.
Madrid: You've allotted more time there than most tourists do. It is fine if you want to overdose on the art museums, but if you are not huge art fans, you may have an extra day. Please believe me when I say that Avila is not worth your time. It has a wall, but you'll be ready to leave within 2 hours if not sooner. (If you must have a wall, Girona is a vastly better choice.) Segovia is a much more interesting destination. And Toledo is magnificent. It is my #1 side-trip in Spain (though I actually spent 3 nights there). Definitely include Toledo. But think about moving at least one of the Madrid nights somewhere else. I don't think you want a car for any of the usual Madrid side-trips. The train will be fine, and you won't have to look for a place to park, or pay for the privilege. You can save a bit of money on Segovia tickets by buying them well in advance if you can commit to a particular departure day and time. Toledo ticket prices do not vary.
Seville needs a lot more than 2 nights, especially if you are not going to make a separate overnight stop in Cordoba.
You need to go to ViaMichelin.com to check driving times from Malaga to the places you contemplate day-tripping to. If you intend to use the train, check the schedules on the Deutsche Bahn website. You'll see that for travel legs along the AVE line (Barcelona-Madrid-Cordoba-Seville), the train is much, much faster than a car.
By proposing to spend so much time in Malaga, I think you're setting yourselves up for far too many day-trips with many, many hours on the road (or on a train or bus). In particular, I wouldn't want to treat Granada as a day-trip from Malaga.
