He doesn't care much about them at first. He even said to Kouki and his classmates he has no desire to put the effort needed to stop them. He only considers killing Ehit because it was Tio's wish and when Ehit makes the idiotic decision of taking Yue.
Hajime and his parents are always referred to in the story as Myu's adoptive family.
Even in the afterstory they are never mentioned to be her stepfamily. Since thats the case, the edit to her page is incorrect.
While common sense would dictate that Hajime is her stepfather due to his marriage to Remia, unfortunately that is not the case in this situation. As even after his marriage, he is still being referred to in the story as her adoptive father.
So the page is already accurate the way it was before.
The same type of edit was made in the past by another user to her page in the past, but it was reverted. So for future reference, the page is correct.