And the answer issssssssss
Yellow and Fix You are both Coldplay songs and Cartoon Heart is from the MX song, Charlie Brown. Well done, Vicki!
All three stories involve women who died (Fleur, Sophia, Walburga).
All three stories involve star-crossed romantic relationships (Lily-Louis, Albus-Sophia, Isabelle-Orion).
All three stories mention diseases (bulimia, cancer, migraines, syphilis).
All three are stories written by Mods or former Mods
Here comes a tenuous one:
All three feature love interests who aren;t English ...
Isabelle is American
Sophia is Irish
Louis is half French
Uhm ... that's all I've got for now.
Can the ssssssnake be stopped? Not at the moment because she's slithering to another victory. The answer is...
The first two fics are a bit obvious but you had to read closely to catch that Walburga dies of Syphilis in Noir House.
But wait, there's more! Our first bonus points are being awarded to the great Equinox Chickerydoodaa for pointing out that all the love-interests aren't all fully British. I didn't notice that!