I have 13-year-old B/G twins. The best advice I can offer is to make sure you take time every day to laugh and find humor in the situation, especially when things get overwhelming... which they inevitably will at some point! My funny story is actually a recurring one:
Twins, being so similar yet different, have very distinct personalities, which has led to many hilarious (in hindsight) misadventures. On more than one occasion, we've ended up at the park or a friend's house, and I've realized halfway through our outing that I've got two kids but only one shoe between them! One will invariably leave their shoe somewhere, often in places we've already visited! So now when we go out, I always keep an eagle eye on those sneakers!
On the days where you feel totally frazzled, remember: This too shall pass, and try to find the humor in the chaos!