I found what I believe to be your man by using these keywords -- William Hughes -- Mississippi -Civil war. There are a considerable amount of hits but I think I found him within two pages. This William Hughes is listed as 4th Miss. Cav, Capt Martin's Company, age 38, he surrendered at Citronell.

William T. Hughes 2nd Miss Cav was not taken POW. he gained the rank of Lt.

Found William P. Hughes at http://www.footnote.com/image/#6841389 This matches your #'s 1,2 &3

Except for the notation that Capt. Martin's Company was attached to this Regt.,I see no other reference that this could be from the Mississippi group.

At this time I have not checkked to see ifWilliam Hughes of the 2nd Mississippi Cav, batt was a POW.

GP