Yes, the two radios can talk.
In a ZB network, you will need one radio to act as the coordinator and the other to be either a router (always on) or an end device (sleeping).
The S2B has limited memory and as such requires a different load of firmware for each of the module types (Router AT or Router API, Coordinator AT or Coordinator API and End Device AT or API).
The S2C has more memory and thus only needs a change to some of the parameters.
If you have the S2B setup as a router AT or API, I would leave it as such and setup the S2C as a Coordinator.
This can be done by setting the CE parameter to 1 on the S2C.
In other words, whatever the S2B is currently, keep it that way. Change the S2C as it doesn't require a firmware change.