Well, it depends on what your definition of incest is; the Flock have known each other since they were all small children and there's apparently romantic interest between them.
In the Angel Experiment, Max crashes into a light pole with the rest of her flock (minus Angel) in tow. All survive the crash, but she, Fang, and Nudge end up being abducted back to the School; Gasman and Iggy both end up fleeing successfully.