"Privates and twin brothers Bartlett and John Ellsworth with brother Samuel Ellsworth of Company A, 12th New Hampshire Infantry"
The brothers Ellsworth were all born and living in Wentworth, Grafton County, New Hampshire when the call for 300,000 troops went out in July 1862. The 12th NH Infantry was quickly raised, primarily in Belknap County, beginning in August, with neighboring towns of other counties adding their volunteers. The town of Wentworth contributed 27 men to the 12th NH, 8 of those having the surname Ellsworth. Four of them went into Co. A, while the others were assigned to Co. K.
About the brothers in the photograph:
Samuel Ellsworth, at age 42, enlisted on 7 Aug 1862, and was mustered in on 15 Sept as a private. Captured at Chancellorsville on 5/3/63, he was paroled twelve days later. He was transferred to the 5th Company, 1st Battalion, Invalid Corps (later the Veteran Reserve Corps) on 15 Jan '64, and to Co. D, 1st V.R.C. He deserted in Albany, NY on 15 Oct 1864, and returned to his wife and children in Wentworth. He died in Plymouth, NH on 22 Aug 1895, aged 75.
Bartlett Ellsworth, age 39, enlisted on 26 Aug 1862, and was mustered in on 24 Sept, a private. He would die of typhoid fever near Falmouth, Virginia on 22 Dec 1862. He is buried in the Fredericksburg National Cemetery. His widow, Nancy M (Batchelder), filed for, and received a pension. They had four children.
John Calvin Ellsworth, age 39, enlisted on 30 Aug 1862, and was mustered in as a private on the 15th of Sept. Listed as missing following the Battle of Chancellorsville on 3 May '63, he would later return to his unit. He received a disability discharge on 7 Sept 1864, in Concord. He was married and would live the remainder of his life in Wentworth, dying there on 9 Oct 1881.
https://www.loc.gov/resource/ppmsca.37120/