At the moment we don’t really know what are their limits but from what we can see they “gave” magic to witches and are naturally immune to it, so it should also mean that the rules of magic don’t apply to them. But I also feel the laws of magic are different from the laws of nature. But what is nature in the first place? Is it a force even above the gods? Is it the power of the gods (are they nature personified)? Is it just only above all except the gods?
The writers need to think about this critically if they don’t wanna wreck their lore because if the gods are nature or in control of nature then that totally contradicts what they’ve said about the Originals and Silas and Cade and Dahlia and the Hollow and Hope. Anyways, if this is the case, they’d be absolutely able to kill the Originals (and anyone else) without needing White Oak. No single person we’ve seen would be able to stand against them.
But if they’re also bound by the laws of nature itself then they would be limited like others and won’t be able to kill the originals without white oak, unless they use the other artificial loopholes to them (like every other mortal has).