It's hard to say, but if Miss Tess is hiding it from us, then it's either very important to the plot or not important at all...But knowing Tess and her attention to detail and nuance, I'm leaning towards it being important...
And if we fantasize some more (knowing that Alexander plunged into the abyss of evil, finding himself under the heel of a mysterious group of powerful women, then went through a lot, but still managed to deal with them at the end)...And what if one (or two) of these mysterious sadistic women were later forced to become mothers, defeated by Alexander and then simply raped by him... And from this Jules and Alessa were born...
And it was quite an elaborate revenge of Alexander, who took revenge on them in this way... because what could be more horrible than taking from mothers their own barely born children?
And one more thing...I have long had a vague feeling that some of these mysterious and powerful female sadists were none other than his closest female relatives...I'm talking about Alexander's sisters (Klara and Karin)...Of course, this is just a conspiracy theory based only on intuition...but let's see what turns out to be the case.
(Assuming, of course, Tess ever does show us these mysterious abusers of Alexander who broke his life).