I guess the gist of the question is whether 2 participants may call the same sub-process (in which they both participate) in a simultaneous manner?
Is it safe to assume that for each call each participant will be redirected to its respective pool within the called activity?
If I understand you goal correctly, there are some errors in your process. But let’s take a step back:
A single BPMN model can describe multiple processes. In your example, each pool is considered to be a separate process. So, you have modeled four processes and not just two.
Secondly, call activities link a process that is called synchronously. In your example, “Called Activity - Pool B” is not suited to be referenced by a call activity, because it starts with a message start event. Processes called by a call activity must include a single none start event.
Thirdly, you need some kind of synchronization between the separate process: “Called Activity - Pool B” must inform “Called Activity - Pool A” about the result of the decision.
