Your question is actually a statement. Do you have a question on how to do it? What have you tried thus far? Are you getting any error messages?
As far as I am aware, you can only have a TOTAL number of 10 forwarding numbers in a Ring Group. Have you looked into Call Queues? I haven't used Call Queues in quite a while but I don't believe there is that limitation.
I think what Lee is saying is correct too that you can simultaneously ring multiple ring groups.
2287 USA based users, 28 different sites, 3800 DID lines - all Polycom VVX500 phones
2018-11-19 We have a need to use this programming setup or something similar to it, for Emergency Notification to our front offices at 28 different sites in the event of a site-wide emergency.
Our requirement:When a specific pre-designated extension is dialed - it will ring the 10 phones in the front office simultaneously with a distinctly alternative ring tone - to alert the front office staff there is an emergency situation (active shooter, weapon or bomb threat or whatever)
Follow our testing progress on this issue here