Probably not. Definitely not twins. There's a good bit of age difference here. But, there seems to be a family resemblance. There's a good chance that they were cousins. It is pretty common to see pictures like these of relatives other than brothers taken usually early in the War before disease or action claimed one or more of them. This picture looks like one from about mid-War.

Of particular note, is the physical contact exhibited by the two men in the picture. In modern times (at least in America) you observe less of this. 19th century Americans had fewer hang-ups about gestures of friendship and affection between men. It was not uncommon that two male travellers would share a bed for the night. Soldiers often "spooned" for warmth while tenting under open canvas. It causes one to wonder why we live in a time where one might be derided for such gestures.

If you look at their faces, are they not brothers? Even twins?

My great-great grandfather was a member of Co. K, 10th VA Cav. I have some postwar pictures of him but none of him during the War. It would be great to find some more that may include him. This picture is of very good quality and very helpful for those who research variations in Confederate uniforms, particularly the shell jackets.

Private Chapman was 36 years old at the time of his enlistment at Richmond on June 9, 1861. He enlisted for the period of the conflict. His Compiled Service Record (CSR) at the National Archives contains almost nothing else, but does include a payment requisition, dated November 5, 1863, for a bay mare killed in action on June 17, and said to be valued at $800. The reverse shows a notation that it was paid on November 17. Confederate cavalrymen commonly brought their own mounts to the conflict, but even with the devaluation of Confederate currency, $800 is a lot of money.