What I'd do is consult an "expert". Someone who works in the market, like someone who works for an auction house or a freelance historian of photography. Any chance of knowing who took them? If the photographer is a "name" they will certainly be worth something. Or try and find a collector of old photographs, who might have an idea of what the going prices are. Bear in mind that they might not be worth much, but take your time asking around and do not give them to the first person who says "I'll give you £50 for the lot." Try Googling "19th century Chinese photographs," or perhaps see if you can find some past auction catalogues on Internet.
As with antiques, oriental carpets, old silver, they tend to be worth nothing when you offer them to a dealer, but to be absolutely priceless when a dealer offers them for sale.
I don't really know what I'm talking about, but this is what I would do.