I have not done this yet but here is a link to photos as sources on profiles and as I understand, for a source photo, place it in sources and link to the Free-Space page where it is located. https://www.wikitree.com/wiki/Help:Image_Types
You can take the ten most important images for each profile and place those directly on the profile page for each person. Then, place other photos and images of documents on the free-space page.
If a document or photo refers to more than one person, just link to each person rather than uploading multiple times.
I just re-read your question - I would not put the link under Research. I would explain each document in the biography (and translate if possible) and then do the link to the free-space page as a source citation which will then appear under Sources.