Others have already given you great advice. And it will get better over time.
But it is total nonsense that old dog wouldn't learn new tricks. Of course they learn. And teaching new things is a perfect way to take her mind to something. And to be honest, it could be very good for J if he could teach Pup. Children really learn many valuable skills while teaching animals. Mostly things like patience, having to stay positive and not show frustration, when something doesn't work right away etc. So it could be a good idea if you would first learn how to train a dog with positive methods and could later teach J to train Pup. Of course you would need to be right there to help him even later so he wouldn't get frustrated and retaliate to Pup, J is still very young. But training animals have always been very useful exercise for my kids, it taught them a lot, same as horseback riding. You just to be very clear, that animal is not stupid or bad, if they doesn't understand what child wants but child has to find better way to tell it for them.
But for Pup right now, one useful trick is to make her work for her food. Best way to put a dog to work is give them some nose work. It is really calming for them. For example if her food is not too messy, you could hide a food in small portions around the house. Or use her food as a treat while teaching her to find something you have 'lost.' Or just teach her to follow the trail (maybe hide and seek with J?)