I mean, the main PC isn’t voiced (unless he’s really fucking quiet), so it’s not like there isn’t precedent there. If you just wanted voice Iris, I think it would work just fine as is. But I also think that most of these other voices could work in some capacity or another if you really wanted to put the work in.
To be honest, I didn’t even realize there was voice acting in this game during my first playthrough, since I usually play these with the sound low and read pretty quickly. Looking back, your Iris comes off as perfectly fine and your voice for Genesis is distinct enough for them to both work in the same scene together. Celeste is somewhat similar to Genesis, but since they don’t share any scenes together it also works as is.
Ember is just… off somehow. She’s obviously meant to come off as intimidating at the beginning of the story and your definitely trying to go darker with her voice, but there just isn’t any real… menace to her. I think she comes off as trying too hard to be actually threatening. I wonder if you might want to try a different accent with her, both to distinguish her from the other characters and give her a bit more to grab onto in terms of character. I don’t even think it needs to be a good accent, since I think it would fit Ember’s character to fake an accent to uphold her multiple identities as an upstanding businesswoman for the public, a motherly caretaker for the brothel and a unfeeling crimeboss for the Council.
And the less said about the Bouncer, the better, in my opinion. It sounds like you used a voice modulator to try to artificially deepen your voice, but it makes it sound like a little kid trying to act tough over a phone call. I’m wondering if you might want to try talking normally but with a bit of husk in your voice, like if you tried to go for a Butch Biker Chick rather than Pete Clemenza.
Now, a big problem with one person voicing everyone is that it is much more difficult to react to the other character’s performance (unless you’re some kind of Freak like Billy West who can switch between a bunch of distinct voices on a dime), which I think is a major factor in what makes acting “work”.
The main problem I can think of with the voices is the volume balance, not just in Mic Gain, but also in how the characters are actually speaking. Human beings will always subconsciously try to find an optimal level of how loud to talk depending on their environment and try to match the energy who they’re talking to. Ember always speaks like she’s whispering, so it would make sense for Iris to lower her voice slightly when talking to her. Celeste is bright and bubbly, so it would make sense for other characters to talk slightly more loudly and appear slightly happier when interacting with her. Again, hard to do with just one person.
Apart from that, all I can really recommend is keep practicing different voices. The best VA’s steal judiciously, so try impressions your favorite actors and cartoon characters and see what your voice is doing when you try to imitate them. Don’t be afraid to cross gender lines when you do them either. Remember that it doesn’t have to be a pitch perfect impression. In fact, it’s probably better if it’s not, because then it can just be a “completely original” voice you can use when you want to.
