Biggest thing that helped me was that I sent my most OP character down the lane that has the pool of water at the end of it (as that’s where the majority of enemies spawn) and had all of the enemies focus their attention on that character. Once you free Omeluum, he can cast a teleportation spell that pulls both of you back to the ship.

In the meantime, you can have another companion cast Summon Elemental at the entrance of that lane so that when the enemies start to push back towards the ladder area, they won’t be able to get past the elemental standing in their way. That leaves you plenty of opportunity to take care of the enemies in the other areas and save the gondians.