If you're using interrupt sharing, then by default when you attach an ISR using InterruptAttach() or InterruptAttachEvent(), the new ISR goes to the beginning of the list of ISRs for that interrupt. You can specifically request that your ISR be placed at the end of the list by specifying a flags argument of _NTO_INTR_FLAGS_END.
Note that there's no way to specify any other order (e.g., middle, fifth, second, etc.).