For me I absolutely think it's Miori who's the weak link. The other two are weirdos, sure, but Miori is much creepier in my eyes with her child-loving tendencies.
No, they don't get together yet. The plot seems to be going in the direction of Miori and the guy getting together, with Mug being the third wheel. They get a better dynamic later but I think Mug might have set the both up.
I think the problem is theyre in fukin high school. If they were all adults we could at least see consequences and how this type of thing affect their daily lives life at work reputation and also outside influences like parents and friends judging them. This is just stupid though.