All the bad parents aside, the worst character was Hasumi. The fact he even appeared in the last chapter must mean he's actually the kind of personality, an insufferable man-child, the mangaka is personally fond of it. There are people like that. Fortunately this was a good enough series that one Hasumi couldn't hope to ruin it.
I don't particularly mind the no romance conclusion. There were enough hints to suggest it would have happened sooner or later. The mangaka decided to limit the story to the core group and how they got over their immediate issues. The plot was pretty scripted every now and then even with that strict limit of the chosen scope, so cramming even more in, like how the Wahei+sisters situation would work if Wahei started dating, would have required a whole lot more chapters. Even if it indeed was an extremely valid point.