Thanks for your early reply.
The suggested solution is not feasible because of following points,
1. We have to assign managerial access/rights to each users to manage categories and user groups.
2. Generally users are not interested in showing/sharing his friends (users) list publicly.
3. It is not feasible to create category and user group for each event.
4. Also one user can belong to only one group at a time. Same user cannot be part of multiple groups at a time.
Is there any alternative way to handle this scenario?

Hello sir,
Is there any way we can share the event with specific users only and it will be displayed on all shared users calendar with shared icon?
Basically i want each user with facility to create contacts/friends list. On event we can share with particular friends only and event can be seen by those friends.
Thanks