So, once Apollo, Artemis, and Athena join the Toril Pantheon, the Bottomless Abyss will inevitably be able to pinpoint their location through the bloodline connection with Gaia and them.
Although these three from the Greek Gods are quite powerful, they're just quite powerful, that's all.
Basically, once they arrive in Toril, they're only at the level of Intermediate Divine Power.
Even if they can remain as united as they are now, they still can't withstand the invasion of the Bottomless Abyss... not everyone can endure a war of attrition against a Demon Army.
The Undead Tribe certainly can... their combat style is crazy enough as well.
As long as the top-tier combat power doesn't intervene, they can completely withstand those Demon Armies, which are calculated in billions, with their legion-like combat methods.
