we need the standby "B author" to be able to handle live request immediately without any manual intervention.
It doesn't work like this. The standby isn't meant as an immediate fail-over per-se. The purpose of the standby instances is to guarantee a live data copy of the master repository and ensure a quick switch without data loss in case the master is unavailable for any reason. It's not instant and it 100% requires manual intervention to get the Standby started as a new Primary. 
Also -- you'll need to be very familiar with re-building a standby instance from scratch when you apply any major update to the primary Author. 
TLDR; Cold-Standby is likely not what you think it is.