I’m a little confused by that statement. I assumed that your aim was to have data from multiple devices (the slaves) displayed on one dashboard in Blynk (the master).
If that is what you want, and there is no master to slave communication, only slave to master, then the master device is the one that requires an Auth token.
The slaves don’t need to run any Blynk code other than calling the Blynk API.
If you want something different, with communication from the master to the slaves as well as slaves to master then Node-Red and MQTT is the best option.
More info on Node-Red and MQTT with Blynk in this topic…
Pete.