Please see the following information on Group limits, max registrations and how Hunt Group works.

• A group is limited to 10 members. More than 24 registrations in a simultaneous ring group will cause the call to fail. 
• A group may have at most, 3 external phone numbers not mixed in a Group of Users.  A group with this setup can only be set as a Hunt Group; Simultaneous Ring will not provide a consistent experience.
• In the case of a Hunt Group: For a User with multiple devices, each registered device will ring independently before moving on to the next User listed in the group. 

Group Setup