You're in remarkably good shape, save for the SAT score (though honestly, unless you're super obsessed, everyone does poorly their first time around). Your GPA is great, though keep in mind that if a lot of it is coming from 9th grade, they don't count that. Also keep in mind there's a limit on how many AP classes they count as weighted when the UC system recalculates your GPA. Only your 10th and 11th grade grades count for admissions (coupled with the "strength" of your senior schedule). If you're taking AP's definitely strive to 1) do well, and 2) take the AP test; it can be very helpful when it comes to placing out of requirements at UCSD, UCLA and UCI. You definitely must take 2 SAT II subject tests, though they can be of your choice (must be 2 different subjects though, so no double history or double math etc...). If you intend to apply for engineering you should take math II and some sort of science. You can take the ACT if you want (I strongly recommend it, since A LOT of people do better on it than their SAT). The UC system takes either SAT or ACT, as long as you take the ACT with writing.
Your senior schedule seems strong. Don't get (major) senioritis and fail everything. The UC's can revoke admissions if your grades drop below a certain level. I think if you're going to get any C's or D's you have to report that right away so they're aware of it and can take action/talk to you about it.
The UC's don't practice legacy admissions (so they say), so you having a brother at SD doesn't help much (though he can probably give you the ins and outs of the university a little better).
You have a great shot at SD and Irvine. Of course, both UCLA and Berkeley (which I would also STRONGLY recommend applying to) are the most competitive UC's and two of the best public schools in the world, let alone the nation, so the competition is INTENSE. That said, you have better stats than I did when I applied (again, save for the SAT score) and I got into both.
Do focus on your essays a bit; make sure they're good, since they do matter a lot more than any college will tell you (and that goes for ANY college you apply to, not just the UC's).
Basically, you have to bring up your SAT score a bit. And of course, the admissions departments at every school are always a bit wacky. But you seem like a qualified candidate. You should also consider applying to Stanford, Caltech (if that's your sort of thing lol), Pomona and one of the Claremont colleges. You should also consider (if you're willing to leave the state) Cornell, NYU, Brown, Duke, Northwestern, Notre Dame, University of Pennsylvania/ Bryn Mawr, Rice, the University of Michigan, University of Virginia, and Columbia/Barnard and pretty much anyone below any of those in the rankings.