Lost in Space was a family show both in the sense that it was intended for family viewing and that it portrayed the adventures of a family lost in… well, you know. Despite this, there is remarkably little reference to members of the extended family of the crew (I know of only two).
In the first season episode “Magic Mirror” Judy is seen to be dictating a letter to her “dear cousin Joan.” We are not told through whom she is related to Joan, but the Alpha Control Reference Manual identifies Joan as the daughter of Maureen’s elder sister.
A number of references to Dr. Smith’s extended family occur throughout the series, but the only two episodes that go into much detail are “Ghost in Space” and “Curse of Cousin Smith.” In the former, Smith seeks to contact the spirit of his departed uncle, Thaddeus Smith. In the latter, he is confronted with his cousin Jeremiah, and both cousins refer to their aunt Maude throughout the episode.
On numerous occasions over the course of the series Dr. Smith boasts of his forebears to impress either the Robinsons or an alien. On one occasion (“The Astral Traveller”) this attempt at boasting of his family connexions backfires when it turns out that his ancestors were the mortal enemies of the ghost Hamish.
Among themselves there is rarely any overt display of affection among the Robinsons. Portrayals of John and Maureen embracing and kissing were early forbidden by the network as being too embarrassing to both children and adult viewers. Will is seen having “heart-to-hearts” with his father on a number of occasions which are usually underscored by Johnny Williams’ family theme. In “Follow the Leader” and “The Anti-matter Man” there are very tender scenes between them. In “Space Circus,” after Will has decided to run away, there is a touching scene where he briefly seeks out his sisters and parents in turn to take surreptitious leave of them, giving his mother a sudden peck on the cheek “for no reason.” Don and Judy have a few scenes where they are seen to take each other’s hands when one is leaving, but beyond a kiss on the hand in an early episode, nothing more.
Despite the lack of overt displays of affection, I think it is a mistake to assume that the Robinsons were undemonstrative or lacked the feel of a “real” family. In fact, I think the Robinsons portrayed a real family insofar as they seemed to take their closeness as a given; it was not necessary for them to assert it or refer to it in words except in unusual circumstances. At the same time, a rather subdued but normal sibling tension is seen between Penny and Will, and on rare occasions between Judy and her mother. Viewed in this light, it is no wonder to read early reviews of the show which praised it for its portrayal of a real family and real family values.