Do you know how to send alerts to multiple recipients from Plesk watchdog2 module? It seems to allow me to enter only one email address.... Thanks
From memory, Plesk's watchdog is just Monit, in which case you could just edit the config files by hand (added alert statements as required) and then settings the files to be immutable so that Plesk doesn't blow them away. This is probably not the best solution in your case though.
If you really must use Plesk's watchdog then create a "mail group" in Plesk with the required recipients and set the alert address to that. Even better would be to not use watchdog at all.