So I've got a couple. :3
Brennen is probably not going to help, let's be honest, so cross him off the list.
Maertin lives with daddy in Nerine but can't really comprehend "bad guys" so if Ivar popped up out of the water and pretended to be nice he could maybe get Maertin to help him? He has water healing. Plus, you know, sticking it to Brennen that he got his kid to help would probably be up Ivar's alley. Maybe Ivar could even convince him to come to Ischia, to "help others"?
Or Noah; she's probably a little adrift since she was mostly relying on Bane being in charge of Loess and if he showed up in the Pampas she'd probably be easy to charm, if a little skittish, and she could try.