Could be diet, could be coat blow, although males typically dont blow as much as females, so generally it isnt as noticeable on their tails. Could be medical reasons, although both suffering I would tend to not think genetic unless they have the same sire or dam ( I cant remember who's from who and if they share parents). As far as the coat chewing, thats genetic, intact males are more likely to be chewers. They can mow down coats to nothing including their own where they can reach it, i've seen on someones sheltie...She thought he had thyroid issues, worm issues, nope turned out he could reach his rear and chewed it...So if you have one chewer he could be doing his own as well as the other one...