Derek
Actually, what you are asking to do is a common problem with BPMN.
The reality is that BPMN does not easily represent joint decisions or meetings. Indeed, the assumption is (as with all Flow Diagraming techniques where activities are represented sequentially) one role or swimlane is always deemed to be responsible for the work (i.e. it is virtually impossible to accurately represent a shared activity).
Using the Group concept is one way of doing it (see previous post).
Another is to create a new swimlane that represents the team. In the end, swimlanes are merely annotations on the diagram (as are Groups).
Actually you might get more mileage if you looked into Role Activity Diagrams as against procedural flow charts like BPMN that are segmented by Roles. RADs model how roles change state as a result of the action and interactions (between Roles) that occur. The best reference on this technique is Martyn Ould's "Business Process Management - A Rigorous Approach". There is also a free Eclipse tool for modeling using RADs from www.instream.co.uk . RADs offer an excellent contrast to the procedural nature of flow diagrams ... they help people see where their contribution fits into the overall collaboration of the process.
Hope this helps - Derek Miers - author of the "BPMN Modeling and Reference Guide" (which I co-authored with Stephen White, the main author of the BPMN Specification itself). I would suggest that you track down a copy (best to get it from the publisher rather than Amazon). See www.bpmfocus.org for the links.