It's an annoying problem with writing - I've got a bunch of characters that I've written, how do I keep them together for the adventure I want them to go on?
In some stories, this can be quite annoying - reading YA novels for example, where the teenagers save the world, and the adults did nothing, for some reason.
I am unfortunately falling slightly into that trap - my characters are late teens early twenties, so not as bad - one could conceive why they'd be allowed to be involved in big things. However, a lot of my characters don't have a ton of reason to be involved in things. Several of them have been imprisoned their whole lives and have little real world skill, especially as they are embarking on a mission to a country (and environment) that they have never been in before.
Complicating this further is that my fantasy novel is based around two nations - a human industrial era one, and a merfolk one in the adjacent ocean. This makes it difficult for the land and sea characters to interact.
So does anyone have suggestions on how to untangle the massive mess that is story logistics?