I believe the global in your one table is fields not variables?
Your relationship set up as should work for showing records in a PORTAL on a layout where the global fields are selected.
If you wish to interact with the records in the portal in another way, the script step Go to Related Record should take you to just those records in the other layout (sort of an automatic "find").
Do you mean with "summarize" that there are two or more same products at one year/Customer and show Sum(Quantity) in report?
if you create a summary field (yes you can create summary and calculation fields in tables with external sources!)
and use my method to Go to Related record, the summary of the qty field can be on a list layout.
Or use this method:
Create another portal, but make it one row and place the summary field in it. When the full portal changes based on your global fields, the single-row summary should update as well.