Hi Vane,
The latest sandbox build (2019.4.4122) now supports onLinkClick and onLinkClicked events.
https://javascript.daypilot.org/sandbox/
It will let you implement this logic but it will also require some manual work (finding all linked events if there are more than two). Also, it will not be able to start dragging immediately - the event click will let you select the events in the onLinkClick event handler and then you can start dragging.
Please let me know if it doesn't work as expected.
There is also a feature called "joint events" (not much documented) which will let you add events to a group that will be always moved/resized together. It's a kind of "auto multi-selection":
https://javascript.daypilot.org/demo/scheduler/eventsjoint.html
So that might be another option.