Joining processes

I am trying to start one process by two separate messages and continue only once both messages have been received - .bpmn files attached. This is sort of a post processing scenario.

Problem: the join will never be reached, because separate processes will be spawned for each received message. (At least this is what I think is happening.) Can I join the processes somehow, maybe by using a different expression for the start message events? Or is my thinking completely off and there is a better (or no) way to get this done?

Task1.bpmn (2.1 KB)
Task2.bpmn (2.1 KB)
Common.bpmn (3.8 KB)