Postby sticky-runes » Thu Sep 03, 2015 4:32 am
Yes, there is a point in the game where Louise explains that you can start using up to three parties while sailing (I assume that you are way past this point now that you have all 4 knights in your army) Place Tal, Keneth, Paula and Jewel into your second or third party, and have them win about 10 battles and you'll be able to use the Knight attack with them. You can switch between your three parties on any one of your turns in combat when you encounter enemies at sea.
And as Antimatzist says, you can arrange a separate party without the hero (so you can choose 4 totally optional characters) when you are about to reach the final dungeon. Elenor will explain this when the time comes.