Draggable Group constrain within parents parent possible?

Hey! I have a droparea-element which is a picture (via Background-image) and I want the user to be able to spawn markers on the droparea-element which they are able to place anywhere in the droparea-element after they spawned them.
So I got a Database entry “Marker” which has x,y, values. Whenever the uses clicks the “Spawn” Button, a new Marker is created via Workflow.
Now in order to get the Markers into the droparea-element, I put a Repeating group into it, which works fine so far. Whenever the User clicks “Spawn” a new marker is put into the Repeating group.
The problem is, I want to constrain the moving/dragging of the markers within the drop-area element which would be the parents parent of the dragging group. When I chose the “constrain movement to parent” option, i can only move the markers in their respective repeating group and not the whole drop area.

Somebody have a clue how I can fix that? Or if there is a easier way of implementing this
“Create a marker via buttonclick on an image and allow user to drag it somewhere on the image”-functionality?

Thanks in advance!