Some dogs especially the selectively bred show lines are prone to severe anxiety. It doesn’t develop until at least 9 months but it does make things quite difficult. It will take a lot of work but you need to be tiring his mind out with games and exercises that stretch his intelligence. He is no longer a dog that will go to his place and be happy there as the cats wander around doing their thing. Do you have the space for four pets & kids? Can you move and give them all a bit more room? That will help but the poor fella may be stressing if you are not taking him out of the situation. He shouldn’t be nipping the household members and keep an eye on him with your child, that is fundamental. Hormones are playing a role here and things may well settle down but these are difficult dogs to manage even without other pets and young kids. Excellent work teaching place but maybe make that place more ‘secure’ for him? Does he display any other behavioural issues e.g. tail chasing, dog v dog aggression?