Does Dr Jonathan Crane have a sister?

Answer 1

If you are referring to Dr. Jonathan Crane of the Batman Universes, then the answer is yes.

It was revealed in the comic mini-series/TPB Scarecrow: Year One that while Jonathan Crane's mother, Karen Keeny, concieved Jonathan with a man named Gerald Crane when she was a teenager, she had another child (a blonde baby girl) one to two years before Jonathan became the Scarecrow (she was a toddler that still slept in her crib when Jonathan "visited" them).

It is unsure whether or not she is Jonathan's half-sister or if they are full-blooded siblings, as their mother, Karen, was having an affair with Jonathan's father after she married a Georgian farmer.

Mind you, this is only in the Year One universe of the comics. In one separate issue, however, it is revealed that Karen had moved to Gotham City and was stalked by Jonathan. In "The Long Halloween" it is mentioned that Jonathan strangled his mother to death on Mother's Day. Neither, however, mention or hint towards his sister.