Mass combat with (mostly) NPCs.

I'm going to be running a scene on a ship that includes combat 15 v 30, which is comprised of mostly NPCs, and need some advice on the best way to run it. Quick background, PCs just completed a campaign where they wrecked the criminal empire of a demon worshipping shipping magnate, and escaped on a galleon. En route to the next port, they'll rescue a group of 15 human sailors stranded at sea who are actually magically disguised orc assassins tasked with killing the PCs and as many sailors as possible - basically a suicide mission set up as revenge by the former crime lord. So it's 15 orcs vs. 4 PCs and 26 (normie sailors of various types, not well armed), all NPCs. Not sure the best way to actually run the combat, since the PCs will probably take 5-7 at once, leaving at least 8 more for the crew.