I think the new Kati "how it began" story has not run it´s course. I theorise something like a bang will be coming in a future chapter. Yes, currently teenage Willi and Leia come across as bullies to the majority of people they knew, with few exceptions like Zoey, Stefan, Dana or Gina. And they had a good or at least ok relationship with the rest of the family EXCEPT Kati.
It is also established in both new and old WIAB that it was something Kati did which drove Willi to flee Wollust.
Considering that the High School Twins currently come across in hindsight as tough Jerks and Bullies, who took punishment quite stoically, what the hell has Kati done that Willi fled the city by night and fog and Leia contemplated it too and was only talked out of it by Willi?
That cannot be just Kati spilling she had seen Willi snogging with his Sis, esp. since it is established like in the old version that Dylan already knew the Twins loved each other more than they should. And while he did not like it, he even lied for them because he is of the opinion that you simply cannot control who you fall in love with.
And what can be read between the lines, neither Leia nor Willi have ever forgiven Kati for whar she did back then. It simply must be big and probably not a single deed.
Another point to remember is that Kati has to be pushed to help examine what happened to their mother. No matter whar happened before, the Twins want to solve the puzzle of their Mom´s "accident", whereas Kati is rather eager to continue the old feud. Even the "No War event" Kati is called out by Miru, why her feud with Willi is more important for her than to help solve the case.
And Gina´s tipp to Miru how to learn about the history of the feud between the Twins and Kati shows the bullying was not one-sided, even if Kati´s view might be a bit closer to what happened. So Willi and Leia´s view of the old times has merrit too. But one thing is sure it was a serious clusterfuck.
