Is there a way to share a collection between two objects?
equivalently, if I use the built-in Excel VBO and get a worksheet as a collection, how to use that same collection in a different business object?
The Foundation Training course describes input and output parameters, have you completed and understood that mandatory training? I suggest that you discuss the design for your solution with an experienced user or mentor (someone should be available to you as part of the standard training/enablement path for every trainee developer).