Man this is actually so crazy. I feel very bad for the mc here. Like bro is just a normal guy. He had to be a good brother his whole life and help the family, every time he had a girlfriend his sister pushed them away or made him push her away, was pressured to get married and then not even congratulated when he did and on top of even that his family that he took care of so strongly and caringly said things that deeply hurt him and made him feel pressured and not welcome in his own childhood home. Even then those are not even the biggest problems. They are the mother and the daughter. Like the mc has never had a child and all of a sudden his daughter starts acting weird and pushing the boundaries and then when he freaks out and doesn't know what to do she plays it off as a joke or as a bonding moment. Then there is the mother which seems innocent but then does what she did with the MCs sister and those hints of her past as well in the early chapters.
And if you thought that that's all, oh no no there is more. First its very clear that he is being manipulated and made to think that all that is happening is normal. Second is that the mother and daughter clearly have a plan for him. Now this is my theory but it seems like (based on flashbacks) the mother was deeply in love with a man. This is shown when she was remembering about him when they were on the beach and she was blushing. I think that the daughter also loved her real father very much (not too sure she may have grown up with only her mom). Something happened to that man maybe he died/left and now they are trying to turn the MC into that man. Basically they want him but not him at the same time. Then as of the latest chapter there comes the supposed real father that may or may not be the previous experiment of the mother and daughter that failed and they left him. I mean dude clearly looks dangerous and mentally not there. He looks like a homeless stalker.
I yapped a lot but the MC has a crazy wife that is still not over her old husband, a crazy daughter, unsupportive family, a cheating sister and to top it all off his mental is slowly being tampered with and destroyed. I hope that i am wrong but for now that's what i think. There are very few manga out there that give me a sense of dread every chapter. Like almost everyone in this manga is mentally deranged or borderline crazy. The only normal ones so far are the MC, his mother, the baby and thats lowkey it. Oh and did everyone just forget how that classmate got kidnaped by her ogre/scp looking stalker to who knows where???
I just hope that at the end of all this the MC has a happy ending man. He just doesn't deserve this.