This subseries consists primarily of letters between members of the Kimball family, although a few folders of correspondence with Fiske's in-laws, the Goebels, are also included. Letters between Kimball and his parents, Edwin and Ellen Leore, comprise the bulk of the correspondence, covering a span of twenty years. These letters also offer the most detailed description of some of Kimball's earliest activities, professional and personal. His discussions of his European travels while a Sheldon Fellow in 1911 and of his research in the south as a Sachs Fellow in 1916 read like journals, recording his daily routines of work and occasional play. The letterbooks discussed in the next subseries contain copies of a few additional letters Kimball sent to his mother and sister from Europe, the originals of which are missing from this subseries.
Other activities highlighted in the correspondence with his parents include Kimball's oral defense given as a doctoral candidate at the University of Michigan. In a May 23, 1915 letter to his father Kimball concludes his account noting that after the two-and-a-half-hour exam, his committee needed only 15 minutes to deliberate and offer their congratulations. In a letter written approximately two weeks later, Kimball explains to his parents his preference to be referred to professionally as "Fiske" rather than "Sidney." His involvement in designing the home on Spafford Road in Milton, Massachusetts for his parents and sister is also discussed in several letters written between 1914 and 1916. In addition to detailing academic pursuits, career choices, and the writing projects pursued by both Kimball and Marie, these letters also focus on domestic issues. As a young married couple starting out on a limited budget, Kimball and Marie corresponded regularly with his parents, making obvious a bond of love and respect as well as financial dependence. Kimball's parents often sent checks and a variety of items, including clothing, housewares, chocolates and home-grown pears. Kimball's correspondence with his sister Theodora also reveals a close relationship strengthened not only through familial ties but from a shared passion for scholarship. Theodora came to Harvard University as a librarian in the School of Landscape Architecture during Kimball's last year there. While at Harvard, both Kimballs became associated with the landscape architect and faculty member Henry Hubbard, whom Theodora married in 1924. Her changing relationship with Hubbard occasionally comes to surface during the course of her correspondence with her brother. Most often in their letters, Kimball and his sister discuss the progress of their respective research projects and call on each other for advice or assistance. Also included are a few letters between Kimball and Theodora's physician and nurse, discussing her failing health.
The folder of correspondence from Marie Kimball to her husband consists of five letters, most written during the earlier days of their marriage. In addition to giving detailed accounts of her days apart from Kimball, this small cache of intimate letters underscores Marie's devotion to her husband. Even the latest-dated letter, written after 32 years of marriage and focusing on Marie's handling of two wandering steers on the lawns of Shack Mountain, ends on a note of affection. Letters from Kimball to his "Mia" are scattered throughout various folders, such as the correspondence files of the "Teaching Positions" series. Those folders also contain letters from other parties written to Marie Kimball, usually in response to her request for their assistance in securing a position for her husband. The largest collection of letters between Kimball and his wife are those concerning the construction of their Virginia home, Shack Mountain, and are housed in the "Architectural projects" series.
Other correspondents represented in individual files are: Emma Fullam, a cousin of Kimball's maternal grandmother; Marie's father Julius and her mother; her brothers Julius and Walter and their wives; Henry Hubbard; Kimball's aunt Harriet Ripley Kimball; a cousin Katherine Kimball, who was also an artist living in Europe; and Marguerite Kimball, daughter of Harriet. His dealings with each varied. For Emma Fullam, who made numerous requests for his assistance, Kimball oversaw the sale of many of her antiques. His correspondence with various dealers regarding these sales and valuations are also included. With his in-laws, Kimball often discussed career matters, as well as some personal issues, such as Hubbard's marriage to his childhood friend Isabel Gerrish, which was Theodora's dying wish according to his June 22, 1937 letter.