OP (dad), married a woman and accepted her daughter into the family, making her his stepdaughter. We'll call her Drake. Dad already had a son from a previous marriage. We'll call the son Josh. Drake and Josh became close stepsiblings. Drake started dating a boy, who we'll call Freddy. Drake introduced Freddy to Josh, and they hang out every week at Josh's place to play Overwatch. Drake brought Freddy to her house, where dad was cleaning his guns, just in time for Freddy to walk past on his way to Josh's room.