Canuck's way is smarter than mine. I'm a gung-ho crazy man and I chose to take them all on.
Here's some general hints that helped me. Firstly, I relied on my torpedoes to pull me through.
You're in luck if the sea is rough. The German ships won't be able to land as many hits on ya as you steam in flank speed. Target the farther destroyer with your main guns and blast away. Resist the temptation to make broadside salvoes, this'll just give the Germans more time to hit you with their shells.
So yeah, what I did was turn on my AA defense, and head for the german destroyers flank speed, RIGHT at them. Ignore the US sub and evade torpedoes if needed. Just steam on in. When you're like a few hundred meters away, start worrying about torpedoes. Don't forget that you have as many torpedo tubes as both of the destroyers combined.

I made a last second decision to bear on him from port (opposite side of the other destroyer, so any of his shots/torps would hit his buddy) and I whacked the closer DD with four torpedoes. Make a HARD turn towards the other one and (not likely, but possible) slam the other with your remaining four. Otherwise, just make a broadside and go behind him as you hit him with your six 5-inchers. You should be able to finish him off before he gets you.
Hopefully during this time you didn't run outta AA ammo (Don't you dare waste it on the destroyers!!) and you shot down the enemy planes as you were concentrating on the DDs. Now go hunt the US sub.

You'll probably be rather knocked up from the two DDs, so your turning won't be as good. But since there's only one sub, go nuts with the DC's.
So that's what I did.