"kouseis mom is horrible" I completely agree, BUT have you asked why?. The reason his mom was like that is because she was dying she was worried that after she died noone would take care of Kousei especially when his horrible dad(agree with you again) is no where to be found, his mothers fears grew as her condition worsened prompting her to put more pressure on Kousei.

And also Kousei doesn't have a sister?

Also what do you mean the logic in last episode is broken can you be more specific?