In theory they’re marketed as Hyundai being more ‘budget’ then KIA and the luxury Genesis.
Hyundai models tend to be a little more expensive than their Kia counterparts
Hyundai is targeted (untill recently) their cars to business and older drivers, Kia strives for a more energetic and youthful image and is the sportier looking. And, as you said Genessis is the luxury brand.