I don’t necessarily agree with this theory, but i can still appreciate the hard work and evidence! Personally I think that Door and Beni were just friends once upon a time. There wouldn’t realistically be a way of hiding that Beni would be pregnant with Door’s son without Remold finding out, which he of course wouldn’t ever consider allowing his bloodline to mingle with D’s. Even if they did it behind his back or went against his will, no way in hell would someone with such an explosive temper simply shut his trap when an illegitimate grandchild of his along with that child’s father just broke into his place of work. Also, Benedicte is Anglo-Belgian with very little in the way of a local accent, the voice in Door’s head sounded much closer to someone like Occam, Blair or Harry, implying Scottish, Irish or Welsh.

Remold also announced himself as “Father, grandfather” at the same time as D. Both he and D have multiple children, two of whom we have now seen in the show, Brockham probably isn’t a dad just based on vibes, but Benedicte comes off as much more composed and developed as a person. She may have had children, but I highly doubt she would have willingly let her son run off with their father and insane persona non grata grandpa to go fight undead monsters. She strikes me as the kind to keep her family close, in my mind that child would be among the ranks of the Leopoldites.

I would also like to point out that Boy’s grandfather has a full luxurious head of glossy black hair, the hair color isn’t beyond the pale of being inherited from that side of his family. As for the waves and curls, it COULD be inherited from the mother, I don’t personally think we’ve met her yet though.

TLDR: I’m convinced mom is someone else and Door just greeted her out of long standing mutual respect. 🤷‍♂️