Scan them if you can without breaking them. I have never done this but apparently you soak them in water then dry them out again flat. They were created in a water process so water is not supposed to hurt them as long as you dry them out some what quickly. Do not use heat to dry them. I would try one first to see if it works.
Then keep them in archive folders made for photos. That will help them from curling and will keep them better than any other method. Still scanning them then sending the scans to other relitives is the best way to preserve photos. Try to figure what is the lowest resolution you can use to preserve the photos. No need using 1200 when 150 will do. 19th century photos don'y have much resolution. Later ones need more resolution.