Photo #4 was taken by V. Shteinberg. There is a possibility that this is Vladimir Shteinberg, who had a photo studio in Dvinsk / Dinaburg, currently Daugavpils in Latvia. Perhaps this photo was taken before he had a studio or maybe he was on the road when the photo was taken. It doesn't have the typical border around the photo with the name of the studio listed on the bottom, unlike his numerous photos that can still be found on the Internet.
His son Yakov was a war photographer during WWI and Civil War, working for various publications.
Mike Vayser