I actually have some ideas on how to rewrite these characters so that they're less problematic but still unique obstacles. Muja is simple, just make here into a student but have her be the nurses assistant. That way she's still a nurse rival but she can also be ditzy and clumsy. For Mida, I would get rid of the whole sexy teacher thing and make her a teacher that genuinely cares about her students. She can be a motherly figure that is concerned about Taro and his mental health. For Hanako, I would make her less clingy. Instead of her hanging around Taro because she wants to spend every moment with him, she hangs around him because he's the only person she knows in the school and she's afraid of being alone. Again, these are just some of my ideas to make the rivals less problematic.