How about an "everybody's grandma" type character, whose real family is estranged from them for various reasons (not necessarily justified, possibly time and space means the family drifted apart?) and she takes it upon herself to mentor and bake cookies for (that type of thing) the crew, provide a listening ear, knits them useless stuff, tries to matchmake all the time, etc?
How about the consciousness of someone's parent with whom they have a strained relationship, stuck in an animal's body? Imagine getting nagged by a parrot for not having grandchildren... (and they're not just mimicking someone they heard, either?
A crewman who is haunted by the ghost of someone from history (not necessarily realworld history). They bicker with each other, but nobody else can see them...yet.
A librarian who's always spouting odd facts, stories from the past that are sometimes surprisingly relevant....other times, there seems like no point to their ramblings.