Well, the friend was the only decent person in that house and he was the only one who gave a little kindness to her soooo I won't judge him as hard as the others (at least as far as we know, I just hope he wasn't consciously playing blind because I'd be super disappointed). The rest of the people in that house treated her badly or simply didn't care about the extreme abuse she was suffering and that's wrong as well (even if I can see why they didn't want to get involved, it wasn't necessary for them to see her coldly, talk behind her back, not giving her food or treating her like a stinky mouse, making everything worse for her. Even that can be forgiven but not protecting her when that b4stard was almost killing her with the wipe or when he tried to abuse her were too much, those extremes can't be tolerated).
IMO the young master needs to be accountable for this matter. Yeah, he doesn't deserve to be killed, imprisoned or something like that, but he has to know all the things his mother did and all the things Tia suffered in his house and make his mom responsible for that (even if she's his mom), that way he can give it a close to this situation.
I also think he needs to break his bubble of "naivety and innocence". I admit he's cute and all, but let's admit as well that even if he's a nice guy, at some point he just let his mother do whatever she wanted because she's his mom. From his pov, Tia was below his mother and that's why he didn't fix the situation as a whole or didn't bother to investigate the situation as a whole (I can understand why and maybe he wasn't fully aware of that, but at the end it wasn't truly nice of him). If he were another servant, then giving her food or protecting her from time to time would be an honest help, but in his case, it's not enough. He's a noble and the heir of his household, he can't play the innocent card and pretend he doesn't hold responsibility because HE DOES.
It was easier for him to pretend to help her giving her food and SOMETIMES stop the abuses, smiling at her when he was in front of her ocassionally, rather than trying to truly help her, for example, stopping her mother's actions and not just playing dumb or the best and most honest way to help her: finding her real identity and giving her freedom. She didn't become a maid on her own will, she was there, treated as a slave, despite showing too many hints of an educated background (which would make her, most likely thinking, a noble). But heck no, it's easier for them and more convenient to abuse her, use her and ignore her.
I don't hate him, I do like his cute side and his intent was cute as well, but in a serious way of thinking, he was just playing dumb and he needs to be accountable for that as well. As a noble and the next head of his house he needs to be aware and should have been aware of all of that. If he's just innocent or ignorant, well, it's time to grow then.
Edit: Tnksm for the chapter guys, I'm truly enjoying this! uwu♥