It’d be more work but you could also share your final draft with those people you quote and ask them to annotate it, either with their original comments or new ones. Then you could pick and choose from their commentary to add to the book. In the PDF, you could make that extra layer of annotation into a digital layer that readers could toggle on and off. If you really wanted to get fancy, have them print and hand write their comments and then send you scans to create a layer of literal marginalia.