This is also what I took from another commentor who helped me get their ending ^^
Split your schedule with 1 class that has Siri ( astrology) and one class with Eleni( either crypto/history/potion), they have 3 that they share ( malediction, combat and practical 101), you can just choose 2.
I suggest you start Siri's route before Elenis since youll be staying with her for most of the day if you start her's first. Talk to Siri and spend time with him but also try to also spend time with Eleni to start her route once youve befriended Siri.
After that once you get the option of "Do you know this man?", pressing yes will set you on the right path to their ending ^^ I wish you luck on gettingthem!
hmmm that unfortunately I'm kinda stuck as well, cus for me it worked out fine. I only did a couple class meetings with him and around 1 or 2 lunches with him then started Eleni's. One notable thing I wanna say that might be the reason why to your problem is choose the boldest options for Siri at the get go, which means rack up a lo of STR from the start then later id say grind til Tuesday to start his route. If you didnt I think that might be the case? If you did then sadly idk what else to help ya with but I wish you nothing but the best on getting your happy ending TvT
Siri has his full guide completed I'm pretty sure ! Check it out here https://docs.google.com/document/d/1PabomRM9NxDZA4lS720NJyy-wBnOM71jnspeEGy-Nzg/...