You’ve to take care and set interrupt priorities correctly i.e. logically less than or equal to configMAX_SYSCALL_INTERRUPT_PRIORITY if your ISRs make use of the FreeRTOS - API. That’s all about it.
You don’t really need to take care about nesting at least regarding FreeRTOS.
To get interrupt prios right e.g. on Cortex-M3/4/7 please see https://www.freertos.org/RTOS-Cortex-M3-M4.html