One license is really two things - the GUI license, to open and use the UI, and the rendering license. So you could, for instance, open C4D in one machine and use the GUI, while rendering on another; but fairly pointless tbh as you won't have IR in the first machine, and even material previews may not render. Anyway, to have two machines rendering at once, you will need two render licenses, one you get as part of the main Corona license as mentioned, then a Render Node is the most economic way to have a second one. Those who have had unbroken subscriptions since before Corona 8 do still have historical extra render nodes, but since then Corona only has the one render license.
PS the second one won't need C4D or Max to be opened to authorize it, as the authorization can all come from the License Server on the main machine (or some other License Server specific machine on the network, if you have it set up that way).