... Shivaram Kumara Cunchala never answer questions.
so, let me repeat some, and I suggest that if not answered, there can be no help
1) why is failsafe not good enough?
2) why do you reject using the watchdog
3) if you are to run 3 parallels where are you going to find the teams/persons to write #2 and #3
4) are you aware that, whatever you do it can fail (there will ALWAYS be some part that can cause catastrophic failure, all you can do is reduce the likelyhood)
5) re 4) which 'failsafe' are you going to add if you are, indeed, going for triplicate.
6) why have you not revealed YOUR method/thoughts/hardware/code (the method/thoughts/hardware/code, not just "I want to do standby controller for emergency")
7) which method are you going to use to verify the "standby procesor" is, indeed, functioning before it is called into action
7) how are you going to ensure that e.g. a power spike is not going to take all 2 or 3 systems out
8) how many watts are your diesel power backup generator capable of
9) Pleaase fill in any other details you might have

Erik