There's a lot of trifectas in the game that reference the 3 Astral magic schools- Star , Moon , and Sun - but are the children of Grandfather Spider one of them?
Star - The Rat: His affinity with Aurora Borealis throughout Polaris, and of course being in Polaris alone; Polaris is the name of the Northern Star.
Sun - The Scorpion: The hieroglyphs in the Zafarian cave prophecised them to "Steal the Sun". Plus, Alchemy has a lot on affiliations with the Sun- and The Scorpion is also depicted as a master alchemist. Which leaves...
Moon - The Bat: And this isn't even by default, it does make sense! The Bat is shown to be a vampire, which of course would be related to night and therefore the Moon. Also, The Bat is said to be a Shapeshifter, which just so happens to be the main ability of Moon Magic.
Could this maybe even hint at Shadow-enhanced Astral Magic in the future?
Re: Grandfather Spider's children and Astral Magic?
It would be a nice touch but unless they increase the Shadow Pip chance it won't a very reliable option as players already struggle to get the Shadow Pips they need for their offensive spells.
, Moon 
, and Sun 
- but are the children of Grandfather Spider one of them?