I understood almost nothing about what you said but I am going to try to help
Tavi is basically a genetic mess, she was artificially made by Jaxon and her Ai friend, she is not a demon or anything that thing was just drugs which showed their worst fear (on Tavi's route that fear is being under control by Tavi, forever and with blatant disregard towards you)
Kait is important, she did snitch your plan but her interference helped on allowing you to escape for real.
There are 2 endings, one where you in the end escape and the other you basically help the Captain, but this is only one route and there are two more planned (Kait's building up a team which is likely Switch, and Captain's route which is likely Dom)