ESPHome nodes indeed allow more than one (even active) api connection.
But are your certain your system stability will benefit from the cascade you are driving to achieve? I kind of doubt that if the primary HA doesn’t even allow stable operation
Better let esphome nodes communicate directly with each others when HA is not reachable. The cherry on the cake obviously would be to do this directly with esp-now which makes even a TCP/IP WIFI connection obsolete.