The baby itself not, but rather that they drove a wedge between Hiroto and chika, plus have put a lot more pressure on Hiroto wanting a child.
They probably were just planning on doing a bit of the latter but chika made things really easy for them.
It was previously stated that powers aren't told to the public directly, in fact no one but the gov and her family knows that the sister has 3 op abilities. Just so happens most girls don't mind showing off their powers.
Yeah, its very lazy and kinda disappointing. But it might have a reason...
It's the stepmom. Sis blames the MC for her death and went from bro-con onee-chan to the current psycho killer. MC says that he doesn't know why she blames him for it and we previously were told that the father disappeared (ran off with some woman according to ghost girl? during first chapter)...
How in the world is Sasae's fault? Sure he went straight for the kill but his father was a scumbag that ruined lives without a second thought, and was about to do the same again.
There's literally no way him getting fucked over by Sasae was the "worst death".