Yeah, i wouldn't trust Medb yet, certainly not with my life.
That being said, so far she was truthful, bad tempered and rude but truthful...the same can't be said about either Kajia and even less from the parents, neither would i trust the templars, at all.
So, i'd say Medb has by far the best chances to earn trust among the ones mentioned above.
As for the family, as far as i'm concerned the family consists of the sister. The parents can fuck off, certainly wouldn't trust them ever again.
Fiona has clearly secrets and some seriously fucked up family from what we heard, but i don't think she would backstab the MC.
Elea is the most trustworthy as of now imo.
Medb - Dangerous, bruttish, honest and (overly?) direct
Fiona - Mostly honest, keeps some things hidden (understandable), but looks to be trustworthy
Elea - Honest, good and the one that seems to care for MC the most. Tries to keep things only friendly until Kaija is definitely no longer MCs girlfriend, so double points there.
Kaija - Everything already said.
Elea and Fiona are my favorites so far, simply don't know enough to make proper opinion on Medb, but like what I've seen so far. Obviously, no love for Kaija whatsoever.
Glad this VN is keeping it simple with main LIs. Too many games introduce 20 of them, and then it turns into complete clusterfuck.
Side girls:
Anissa - Like occasional fun scene with her. She's fun, but not relationship material.
Boss - Maybe for some stress relief, but not overly interested in her.
Pub girl - Good looking, wouldn't mind bit of fun (and considering preview renders, going to get it for non-Elea/Fiona route)
Cowboy lady in Neverwhere - Kaija's friend, not interested.
Honorable mention:
Sister - She is amazing and deserves lots of head pats.
Did I miss anyone?