Here is Report Layout
You'll need to describe the underlying data model--the tables and relationships used in more detail.
Do both portals refer to the same Tutorial: What are Table Occurrences?? What relationships/portal filters have you set up for your two portals?
I have the converter portal and scrap portal relationships to the invoice data table. The converter portal pulls converter type and pricing from one a converter table and scrap portal pulling from a scrap material table.
There seems to be an error in your relationship. From the screen shot, it would seem that a "unique values" validation or other field option has been set that limits the value of Invoice Data::Converter to unique values. That would keep two different invoices, for example from having a record in Invoice Data with the same value in Converter.
IF there is one and only one record in converter linked to any one record in Invoice Data and one and only one record in scrap linked to any one record in Invoice Data, then you can set up fields in the body of your invoice print layout to include fields from both Converters and Scrap. But if a multiple records in Converters or Scrap can link to the same record in Invoice Data, this won't work.
You can either place a row of transparent field from one of these two portal tables directly on top of the other, or you can set up a double row of fields in the body, one row for each table and set the bottom row of fields to "slde up" and to "resize enclosing part". This "sliding", is only visible when printing, previewing or saving as PDF, but that should suffice for printing an invoice.
To get the field labels, you can put text inside a sub summary layout part and use either calculation fields defined in Invoice Data or layout text with conditional formatting to get a set of column labels that is correct for each group of invoice data records.