Obviously we can't just flat-out romanize them then, since the difference between the two would be lost. The kanji here is more important than the reading, if you encounter them in-game their class is labeled with just that final kanji (oni-class or hime-class).
As for the -symbiotic thing, I think that's more of a description than an attempt to directly translate it; you have the humanoid abyss girl and then the hulking monster that together comprise the 戦艦棲姫. Although unlike the others that have 棲 paired with a location (i.e. anchorage-dwelling oni), here it's battleship-棲, which could suggest that she lives with/is part of the battleship creature.
Locutions like this are always so fun to come up with a "correct" translation.