It wouldn't shock me if Jenna/Katie had a shared route. MC can tell Jenna that he fooled around with Katie, which was only half-true but Jenna didn't mind. She just wanted to be sure MC wasn't leaving her.
Katie already has a sharing route with her friends. Is Jenna that big of a leap? Maybe, maybe not.
So, a Katie + Jenna route is probable. Maybe not in romantic relationships, but Katie has a FWB route too. That one is much more likely.
However, I still see no way of including Monica in that mix. Although MC could flirt with them all during the movie night, and you could thread the needle to keep all 3 routes going in a few different ways. But if, somehow, someway Monica can also be involved then it'll be a very difficult thing to do, so choices still matter a lot you'd just have to have everything perfect. 9 routes lead to a bad end and that final would lead to something more.