I have a couple problems, and I'm honestly not sure what the issue is or where I went wrong.
First issue, I had the strategy meeting about the party and I broke up with Isabella (if memory serves, I accepted her advances and broke up with her to attend the party, and I went with the decision to drug the party, can't be sure as it's been a little bit.) However, I have no option for anyone else to talk about the party and no hints to trigger it in any fashion. I saw the name Yua come up a couple times while looking through posts here for advice but I can't find anyone with that name.
Second (and possibly related) issue, I am missing some slots in the side character roster. Four in total, what am I missing? Am I going to have to restart entirely?