Will wrote with two questions:
Some 15 years ago, someone in the family lost the lone original of a cherished family photo from 1880. We have the photocopy in black and white. First, could this be turned back into a negative (albeit an inferior one) and reprinted using antique sepia techniques from similar family photo’s taken at the same time in the same 1880’s studio?
Well, that really depends on the quality of the photocopy. If it’s clear enough you could scan it and try to enhance it using photo editing software or you could hire someone to try to improve the quality. I’ve scanned high quality color photocopies with a good result, but if your black and white copy is muddy you’ll have to start by fixing the contrast in the image.