You appear to have this relationship: Order>-----Products where ProductID is the match field linking the tables. That seems to have a table missing as an order record usually links to a line items type table where you have one related record for each product ordered, but sticking with what you describe, you should link Products 2 to Order by the Product Group field and only the product group field. Then update your value list definition to specify Order as the starting from table occurrence. (and if you have a line items table, substitute it in each place where I've specified the Order table.)
Thank you! That solved my problem. I really appreciate your help!