[Armistead]

Merchants...

I would just fire the two at the largest target and evade, saving the aft. You may miss, have a dud or two may not sink it, so you'll have one to finish it off. If you want to be risky, try a 45 degree approach, so you'll be halfway turned around, fire two at one, come around and fire stern at the other. If you don't sink them, maybe you'll damage them enough they'll fall way behind and you can finish them with the deckgun.

The ships could be loaded with ammo. If you know what cargo looks like, such as ammo crates on deck, one will do the trick.