This comic is super unclear so:
On the left is a 'good' timeline where Lina never died. In order (read straight downward) Lina and Anna (and Marvin) at the windmill. Lina's birthday. Rainer meeting Mike for the first time. Lina, pregnant with Paul and having adopted Tiara. Lina, coming home with Paul. Paul and Tiara playing. And then Mike's death.
On the right side is the more canon Petscop timeline with Lina being gone at the windmill, Marvin sitting on the bench on her birthday, Anna and Marvin's wedding, Anna pregnant with Carrie, Anna coming home with Carrie, and Marvin quietly abusing her. Again, then Mike's death.
The idea is Mike's death is a kind of 'canon event' and the fact that both timelines were experiencing the same situation at the same time created a kind of crossover point where, in the ensuing chaos after Mike's death, Tiara and Paul were accidently jostled from the left timeline into the other timeline.