If your receiver supports the corresponding Atmos outputs, it's no problem. Without Atmos channels, these speakers make no sense, so you're better off with an additional pair of surround speakers.
No, they don't have to. Which AV receiver do you have? And which speaker system?
I read from your text that you want to swap the current surround speakers with the Onkyo.
Do I understand that correctly?
The Onkyo are Atmos LS and belong on the front LS or the surround LS and should radiate to the ceiling.
But it could be that I have misunderstood :)
MFG