As I stated each has its own database.
Thats not ok as I explained above. A system requirement for ispconfig is that you have a local and separate mysql server on each server and that the local ispconfig database resides on the local server. ISPConfig takes care to replicate its own database content. If you activate mysql replication on a ispconfig database, the the system will fail. ISPConfigs own replication mechanism is fault tolerant and can be used for high latencys as well, it supports also server outages of up to 30 days without sync problems.
Your current setup can not work for ispconfig, so please read the two multiserver guides again and install ispcofig accordingly.