I think you're doing a great job with Chibiusa so far, and have no crit to offer for her, just a general gushing about how cute and charming she is. It never comes across as forced or strained... it all seems perfectly natural, and it's clear that you're at ease playing her and have fun playing her, too. It was a good choice and I can't wait to see more of her!
I do have some crit for Athos, however. I think in some ways you play up Athos' insular nature a little too much? I feel like he's almost too idle, and perhaps part of this is just because I haven't seen him interacting much beyond Porthos and Aramis, but Athos is the leader of the three, he should therefore be pretty good at gathering information, interacting with others, at least on a professional basis, and taking charge. Instead, he seems to fade away mostly to the background and only seems to interact with others when he's drowning himself in alcohol.
Not that I don't think that's on par for Athos' character, and certainly when put in a stressful situation he feels powerless in, but at the same time, Athos as you're playing him now presents more like he's from the intro in the first episode rather than his canonpoint at the end of episode 10. He's grown a lot throughout the first season, and has a new standpoint after the confrontation with Milady. He's a little freer, perhaps, a little less guarded. But this doesn't come across at all in the threads he's in. I'm not saying he's going to be as interactive as Chibiusa is, but I feel like his general introverted nature is used as a reason for not tossing him around, when in reality he should be tossed around more than he is. If you're unsure where to start, both Porthos and Aramis have extensive CR that he can bounce off of, and there are plenty of compatible characters with his personality type in Kiseki, as well.
I think you do a fantastic job capturing Athos' voice, but as it stands, he seems far too reliant upon Porthos and Aramis. Which, again, isn't ooc on its own, but when coupled with the lack of interaction with others, the lack of acknowledgement of Milady, d'Artagnan, Paris itself, or anything of the like, he seems to exist mostly in a vacuum, when, despite not being as cheerful as Porthos or Aramis, should still be able to exist independent of them enough to develop his own CR and interaction with other people and the world itself, especially as he's the leader of the three.