The SMP version of FreeRTOS schedules tasks to ALL cores in the system. That requires that the each core have access to the memory required by any task. Even the kernel task list must be shared between the cores. This requirement forces each R5 to have full access to ALL the memory.
If the R5’s do not have shared access to all the memory, then you can run 1 instance of FreeRTOS on each R5. Tasks will only run on a single R5. In effect you will have multiple applications running and each application will have its own copy of FreeRTOS. In this system, any communication between R5 applications will need to be handled with special features in that SOC.