Find Parent Event of Child Event

Problem Statement

Show a list of events on visualforce page, and give ability to respond as accept/reject/maybe.

Scenario:

• 3 users are participating in an event.
• Event is created by a user named “Ab Jindal” and he invites two other sfdc users i.e. “Ab Dev” and “Sm Dev”
• Here is event data with parent event and eventrelations created for owner “Ab Jindal”
  
• EventRelation table data for this event:
  

From above screenshots, its clear that one needs Parent Event Id to update any EventRelation. Even if we try to hack and create a new EventRelation record via invited user i.e. “Ab Dev” or “Sm Dev”, it will fail. Here is sample failure code

EventRelation er = new EventRelation(
                           RelationId = UserInfo.getUserId()  ,  
                           EventId = '00U2000000VcrubEAB',
                           Status = 'Declined'
                     );

insert er;

Here is the error which comes on executing above code:

System.DmlException: Insert failed. First exception on row 0; first
error: INVALID_OPERATION, You cannot create an Event Relation with a
child event.: [EventId]

So, I wanted to know either of following two questions:

• How we can get parent event id from a child event ?
• Or, how to update child event with accept/decline/maybe info ?

Similar Questions

On researching found this post which is somewhat close to my challenge, but is not having correct resolution.