Man on left is unidentified; on right is Andrew S. Knight Photo taken before 1877 when he married Clara Young Enlargement was made from a photo made from the original deguerreotype.
The other man wears a uniform hat, an earring, and a pinky ring.
Grandpa has a pinky ring and no wedding ring. This is the only photo we have of him without facial hair.
They appear to be playing hearts.