You can add users to your main account in myopenhab.org. Don’t create a whole new account as each instance of OH can only be connected to one account. When you log into myopenhab.org, hover over your email in the upper right and click on Users. You can add users from there.
Then just make sure to use the appropriate notification Action in your Rules. See Actions | openHAB which documents there are Actions to send a message to a specific user, broadcast to all, or just log the notification which will go to myopenhab.org and appear in the list but not get forwarded to any phone or device.
I recommend looking at Design Pattern: Separation of Behaviors for a way to centralize your alerting so that you can play around with different strategies without needing to make changes in all of your Rules.