SPOILERS: and a reading recommendation
SPOILERS:
Their surrogate mom was clearly Fate (the incarnation -- the actual FATE) - and in the course of the show, she turned that role over to Jacob.
I'm sorry that some are disappointed. I, for one, started to worry that this was going to be tied back to JUST Egyptian, or JUST judeo-christian mythology. I was hoping it would be bigger than that.
Fate is one of the most interesting mythological characters. Fate is really three people:
Clotho spins and separates the threads of life
Lachesis weaves the threads into the tapestry of life
Atropos measures and cuts the threads (ends each life).
For some interesting reading, check out Piers Anthony incarnations of immortality. An incredible series of books (8) about Death (Thanatos), Time (Chronos), Fate (Clotho / Lachesis / Atropos), War (Mars), Nature (Gaea), Evil (Satan), Good (God(dess)), and Night (Nox).
Anyway, as we've been speculating over the last few weeks / months, Jacob isn't really "Good" and MIB isn't really "Bad."
In Anthony's books, Satan isn't "really" evil. It's just his role to be the incarnation of evil - a role he enjoys doing well.