Control multiple homes using same MQTT server

I'm building home automation system using the ESP8266 and MQTT. I have 3 homes to automate but, I don't know how to move forward with that. I have searched online for this but found videos and tutorials only for one home. I want to control 3 homes with same MQTT server. So please let me know if anybody knows how to do this.

Thanks in advance

What's a "home" in that context? Usually one human has only one home although she might have multiple houses.
If you have a house where you live, a holiday house and maybe a hunting lodge, these house usually are quite apart from each other, so using one server for all of them is a bad idea. It's a much better idea to have one server for each house and may do some aggregation on the server of the main house.
But having ESP8266 communicating with the MQTT server of the Internet is a bad idea, the MQTT server of your houses should not be accessible from the Internet.