That's a nice trifold frame, but something with a window mat would be better for the future to keep the photo off the glass.
The frame has the photographer's name on the back, so I'm fairly sure they've been in the frame since the 30s, too.
I do intend to go from least destructive on up and start with photos and, um, scanning maybe, and then try to separate them. I don't even know if I can get the photos out of the frame with the glass - the glass may be attached to the frame edges for all I know. I know I won't be rushing it - I won't get a lot of time or chances to work on them as it is and they've been sitting this way since last summer or so.