The men you asked about were: 1) Elmer R. Culver, b. 1836, Athens Co., OH, d. 1928, IA, was son of James S. Culver and Maria Lottridge. James S. Culver, b 1802, OH was son of Roswell Culver, b 1773, NY and Lydia Hatch, b. ca 1775 NY. Elmer Culver called James C. Culver "brother" in his letter dated 1889, and gives details on his brothers and sisters.
2)Ellmer Barrows, b. ca 1834, OH, marr Letitia Ermine --. In his letter dated 1862 he calles James "cousin".I realize the "cousin" could also be Letitia Ermine since she added a note to the letter calling him "cousin".I do not know her last name.There are Barrows - Culver marriages. Ellmer Barrows was a son of Henry Barrows and Sally Ballard.
3)Charles Richardson, b ca 1839, Athens Co., OH, d. 1887, MI.He marr Mary Robinson, b ca 1850, b. MI.His letter is dated 1865 and says he is at Elmer Barrown to work on his land.[James C. Culver had land in MIadjacent to that of Ellmer Barrows and Charles Richardson].Charles identifies himself as "cousin" and "brother Mason". Charles was a son of Salem Town Richardson and Lorinda Cross, both born in Athens Co.OH.
4)Return A. Miller, b 1838, d. 1862 in Athens Co. OH.His letter, dated 1861, calls him "cousin" and mentions relatives. Return A. Miller was a son of John S. Miller and Sophronia Barrows.
Does this give you enough info to look for connections to your family? I do have more info on all these people including their ancestry and other children.
[Letitia Lamon Culver was dau of Joel Lamon and Phebe Jaquith.Both those families have names not continued for generations].