Hello Atlassian Community 
I have a difficult question today.
A user would like us to create a central board which connects all issues from another 5 Jira Business (company-managed-project).
The idea is that this central board holds the "Epic" ticket and the other boards hold the child (linked) issues on this central board a user will be able to go to Timeline and see at which stage the child issues are at the moment.
Example:
The "Epic" Issue is called the Xmas 2023 Campaign:
and under it, there will be different "child" issues e.g. photo production board have a photo shoot child issue linked to the Xmas 2023 campaign in the central board.
The question is what is the best way to link those issues to one main issue on the central board and all of them reflect on the timeline at this central board?
Jira software is not an option for cost reasons and we have backbone issue sync.
Would some suggest me any idea on how to do it?
Best, Lucas.