"We become who we are because of those who came before." ~ Kathryn Smith Lockhard
Can you enlarge the picture to read the poster on the window? If so, that will let you know if it was an English or German speaking country. I have two unknowns myself. I know they were my fathers Irish side because they were all together with his family.
Do they resemble anyone else in other photos? I clicked on the picture to get a closer look but lightbox doesn't enlarge it much.... I am amazed that you have only ONE photo with unidentified people. That's amazing to me!