Read this book in the 80s as a kid. All I remember is that it was sci fi, spaceships were in several settings, the twins were a boy and a girl, and they were psychic.
Could that be Robert Heinlein's Time for the Stars? It is discovered that some pairs of identical twins are telepathic between themselves and that telepathy is instantaneous and unaffected by distance. Pairs of twins are hired to accompany the first interstellar expeditions which set out in different directions in a dozen STL torchships. The book follows one shipboard twin as he visits several planets in turn and as his stay-at-home twin ages while he does not (due to time dilation.) In fact, as his stay-at-home twin ages, he learns to do the telepathy with the twin's descendants, ending with a grand-daughter.