Not like Rei should not take care with this guy, entering as a "strange" in this kind of situation...
But my relief is that this father looks to be a real coward, for example, not involving his own parents to help him and trying to fool his daughters. And it is placed in Japan too.
In other countries the same kind of situation, messing with a toxic ex-husband (or "ex"-father in the case) could easily ending up in tragedy.
This route is not impossible in any japanese drama, but come on, this is a story about shoji and stuff too, with moments of comedy. Would be a total switch of genre if some tragedy happens, to worse, destroying the magic of this series.
But in other mangaka/writers hands, they would be trembling to do it, since the death flags now would be toooo high.