The Reuben Johnson who was bondsman for William W. Johnson and Patsy Johnson was the son of Amos Johnson, Jr. (will proven 1824) and grandson of Amos Johnson, Sr. (will devised 1797). Amos, Sr. was the much older half-brother of Moses and Starling Johnson. Their father John Johnson (will 1780) had two sets of children, a much older set probably born in the 1730s and 1740s by a previous wife, and a younger set born in the 1750s and 1760s by second wife Elizabeth (will 1790). Amos, Sr. was by the first wife (identity unknown). Moses and Starling were by second wife Elizabeth. Amos Johnson, Sr. was married and having children himself by the time his younger half-siblings were born.
In short, William W. Johnson and Reuben Johnson would have been half first cousins once-removed. Reuben's father Amos, Jr. (d. 1824) would have been William W. Johnson's half first cousin. However, agewise, Amos, Jr. was contemporary with William W.'s father Moses Johnson. William W. Johnson was also a witness of Amos, Jr.(1824)'s will. Amos Johnson, Jr., indeed all these early Johnsons, lived between Swift Creek and Middle Creek in present day Cleveland Township, Johnston County, NC. Most of their land was on Mountain Branch. Some of Amos, Jr. (1824)'s children (e.g. Allen D.) acquired land further south in the Hannah's Creek area of Johnston County as well.