Man, I love this manga because it brings reality. We all know Ercella isn't the best mother, but she wishes the best for her son. On the other hand, Harsen decision indeed kind of rash. If your daughter in law in future end up being no good, it eventually will bring down your son and the family...
I honestly have really hard time with guessing.
I thought glasses girl was sus af, but she might be the lying girl. Remember the lying girl believes in her lie that it becomes her part of identity.
Also, business girl sus, she might be the one tied with violence in sex since she avoids it so much.