Carolyn's keeping Joe out of the family: she told him the lie that her mother told Carter about Roger's accident. That's probably a good thing, because Joe, having recovered miraculously quickly from his drinking bout, has gone back to his Boy Scout ways. If Carolyn had told him the truth, would he have walked into the Logansport movie theater (I'm betting Collinsport doesn't have a cinema of its own) and told Carter there still was a criminal on the loose? This is still that same evening, right?
Incidentally, I don't think we ever hear anything about Joe's parents. It seems clear that he's a Collinsport native, and the parents must be reasonably respectable, or Elizabeth wouldn't want Joe as a son-in-law. I assume they're dead; if they were alive they should have gotten mentioned during the talk of finding a way to pay for a boat.
