Want to create a Zigbee network with selective connections

[@ADEngineer]

Hi, I want to create a Zigbee network where only selective end devices can connect such that if two networks are in same channel then the end device must connect to the dedicated network only. I have this fire alarm system where each building has its own network.

All the coordinators are using same channel but different pan ids. I want to my end devices to connect to the specific coordinator. I don't know which instructions are to be used for this. I have already designed basic end device and coordinators with dedicated PAN IDs.

Need guidance...