The only thing I know for sure is that you need to be on the Others path and that you do not get the blowjob from Heather during Halloween. Other than that there might be some hidden requirements that are easily gotten if you just do any positive thing possible with Elena and JB.
I didn't even realize that at the campfire. If I'm not mistaken, Camila and Riona were the only side girls that say in a way they want the relationship to end and after that want MC to look for them.
During Episode 4 in the party at the DIK's mansion when Cathy's cluck gets revealed, if you fucked both Mona & Camilla in the bathroom Mona ends up blurting out drunkenly to Camilla while MC is right there that she wants to fuck MC too. Implying that Camilla told Mona that she wanted to have a go with him (again).
And in Episode 5 Camilla even goes on to say that she finds MC attractive and she wants to have fun with him too, no strings attached.
I think that Camilla is the Sarah equivalent while Riona is more so the Melanie equivalent. Camilla and Sarah don't have any drama issues as far as we can tell, they're pretty chill and...apart from being student prostitutes, pretty normal students all around.
However Melanie and Riona seem to be constantly trying to hold things together. They are a lot more sensitive and emotional. Their personalities blend together more as time goes on.
Might be reading too much into it but that's just my basic analysis lol.