Since it sounds like he didn't live in Gordon for a few years and then showed back up at the cabin after he was 18, I sort of wonder if JP lied to the neighbor lady and said his parents had "abandoned" him and he had been living in foster care with his brother? It would be the perfect lie to tell to try to get sympathy from a neighbor asking why he was back living there without his parents.I see JP as the type who would always make himself out to be a victim even when it is not true. JMO.
My other theory is that his dad was supposed to be taking care of the boys but something happened that made foster care investigate and take the boys away for a time. It could be something one of the boys did that is now sealed as a juvenile record/CPS report or it could be something the father did that lead to the boys being taken away (I won't speculate on the father as that would be against TOS).