If this is indeed the family of Sam Watkins, author of "Company Aytch"; he likely could have gotten out of the service, especially earlier in the war.
As he enlisted very early in the war, and stayed until the final surrender; this shows him to be a true and gallant soldier who was dedicated to the cause. More so than any who were from privileged families, and did leave the army.

The narration in Ken Burns' film mentions the fact that Sam was so anxious to join the army that he left before his brothers. The film does suffer from questionable accuracy at times, and I can't remember Sam mentioning his brothers in his book, but I haven't read it in a number of years.

I would be curious about the service of his brothers. Were they as dedicated as Sam ?

D.W.