Preface: Given the information that is available (which is always subject to change), I'm currently of the opinion that the mother does not appear to be the a "go-along-with-the-husband's-evilness-because-she-is-too-cowed-to-stand-up-to-him" type of wife, but rather someone who is actively and willingly complicit in a horrific act. There are, unfortunately, zillions of cases where one of the partners is the active perpetrator while the other plays a more passive role, but this doesn't seem to be the case here.
Which brings me to my intended point - HOW did these two people find each other? I understand that there are many, many individuals out there who are capable of unspeakable atrocities, but for two people capable of such horror to "join forces" is just amazing and terrifying to me.