It can be inferred that the Bolt brothers immigrated to the USA from Scotland with their parents as young boys; when they receive a surprise visit from their Uncle Duncan (their father's twin), he reminisces about last seeing Jeremy as a toddler, and they reminisce about the old family estate in Scotland, as well as commenting that they never expected him to ever leave Scotland.
Capt. Clancy seems older than Jason Bolt, but in reality Henry Beckman and Robert Brown are about the same age. Likewise, Denver Pyle, who played the Bolt brothers' Uncle Duncan, their father's twin brother, was only six years older than Robert Brown.
The characters & setting were used for the novel Ishmael by Barbara Hambly, for an enjoyable novel about Spock (of Star Trek) saving the future by saving one of the characters, but the effort to get there leaves him an amnesiac & with a leg injury that restricts his mobility.
In response to a couple of the comments on here; one states that Mark Lenard plays an ancestor of Spock's mother, Amanda Grayson. This actually comes from the Barbara Hambly Star Trek novel "Ishmael" and NOT from the series itself. Hambly made that connection at the end of her story. The other comment is also related to "Ishmael." This commenter states that Spock is sent back in time to save a character, when the Klingons send him back through the Guardian of Forever in an attempt to disrupt the timeline that causes the formation of the United Federation of Planets.