From what I understand, the patriarch, Junius Brutus Booth, left his first family in England in order to run off to America with Edwin and JWB’s (and their siblings’) mother. He was still legally married to the first wife. So, JWB and Edwin and their siblings were illegitimate. Years later, the wife and son from the first marriage tracked them down and sued the Booth patriarch for years of unpaid support.They threatened to cause a giant scandal that would ruin Papa Booth’s ability to ever earn a living again as an actor. Papa Booth had to pay them off in order for them to leave him and his second family alone and to finalize the divorce.John Wilkes Booth's father also had a family he abandoned in England before immigrating over with his mistress (who was the mother of John Wilkes and his siblings.) I think one of the sons from the first relationship survived into adulthood, but I have no clue if he had children himself.
JWB got teased at school for being illegitimate when he was a kid.