They are girls no women and it´s not Josei.
Pretty sure the FL is a college student and has a job and (tries to) help her sis pay rent, so its safe to say she's a young adult woman. Also, why did you bring up Josei??
Yeah, the MC is in college (age-specific 21+ because in ch 5 she drank alcohol)
Prez is roughly 26 ( highly likely the same age as MC's sister bc they were classmates)
And the exhibitionist cosplayer is 18+ that's for sure. They're all adults I'm pretty sure.
As long as theyre both two consenting adults, its fine....maybe??