Records that contain several sub items

We just need a certain view of the form and report, see photos. First, they create the PO and add the Cost Items. Then there is a button Add Bill showing the Bill Form where they should see the list of Cost Items in the grid edit of the embedded report (is this possible?) and be able to add Bill %. The embedded report is from the Cost Items table and doesn't work because the Bill % will only show the latest update instead of showing the different Bill %. Don't mind the Line Item Bill Summary field and empty fields in the form for now. Just need help on how to make this view possible where each Bill record shows the list of Cost Items with Bill%. Examples are Bill#1 ($85) and Bill#2 ($165). So this PO record has 2 Bill records.