The mother has to be weird somehow.... But I don't remember what violent tendencies she has, and in this chapter she truly seems oblivious...?
Edit:
@MarqFJA87 point taken. She's not completely oblivious. She knows her husband is a criminal.... But she's just serenely okay with that? She doesn't have any sort of Yandere tendencies like all the rest of her family? She definitely can't be considered normal.... But I wonder if there's more to her abnormality.....?