I know for certain the man on top left is Charles Southard.  I believe the lady next to him is Ellen Dowland Southard.  Even though the photo is not labeled, this is the second time these two have shown up together in a collection.  There was about 25 years difference in their ages.  By the graphics on the card, I think these were taken about 1880.  The bottom two are unidentified and I have no idea who they are.