Can I have caller id on more than one tv?
Yes providing the service on the 2nd box supports it. See the following:
See this for X1 https://www.xfinity.com/support/cable-tv/x1-text-messaging-notifications/
Or this for legacy cable https://www.xfinity.com/support/phone/settings-for-the-universal-caller-id-to-tv-app/
If the above does not help, call into Comcast at 1-800-266-2278 or 1-800-934-6489 and speak with a CSR to ensure the CallerID Rate Code is active on your account.