Now this is slice of life... no weirdly smart mc... but i guess in a way this mc has something like that like what he said... he was lost... fine... background story is important for a story... but yah mc being quite realistic like how he would get mad at them... more please...
I feel this will go incestuous with the older sister. She is portrayed more motherly since she has to look after her younger sisters and he is the salary-man of the family so there is a married couple dynamic here. I wouldn't be surprised because Japan.
@Sola Wahei has been throwing them out since the beginning, so she probably wants to proceed as if she was walking on thin ice. Being a kid, she wouldn't be wise enough to realise that if she's inconvenienced by some things in her daily life, it might also inconvenience Wahei himself, making matters worse. Seeing how the dude attempted to develop the perfect home for himself, he wouldn't actually want to see anyone living a half-assed life there.