Not entirely sure what the point of the sidekicks are either, other than as a way to get around party size limits. Some of them appear to have interesting backstories that could certainly be made into very interesting stories and quests.
Ydwin: An animancer who is on the cutting edge of Forensic Science. Her insight into things alone would be interesting.
Bonteru: Hiravias would find him to be a fellow explorer. Though I'm not sure what sort of story he would have.
Radora: mmh, sounds like the standard trope of troubled drifter.
Rekke: Now, this guy has LOADS of story potential, someone who is clearly not local to the Deadfire, or any known culture, wears strange clothes, speaks a language nobody knows or recognizes. Perhaps you, the watcher, can glean into his past, or in your explorations of the Deadfire, you find clues to his past and identity, perhaps find a way to communicate with him, etc. SO MUCH potential. Of course though, having him as a sidekick could satisfy that kind of thing.