Your son has purchase a cross between 2 highly intelligent working breeds . Training needs to start from day one and go on every day of its life. It’s not to let to start using a crate but not as a place to lock it in to keep it out of trouble. That’s not the purpose of a crate.
The whole mouthing thing is all about dominance and attention.
Distraction is a good tool , offer the dog something exciting ( not a run of the mill toy, something special) . Withdraw attention which is what it’s seeking , if it jumps up at you , turn away, don’t make eye contact .
To be fair , it might be worth getting an apt with a behaviourist to get a handle on all the things your son could and should be doing .
Even after many years with dogs , our current dog had anxiety issues and we had a behaviourist come to the house , observe us and the dog and the solution was so easy we were amazed. It wasn’t hugely expensive either. One thing he did recommend you could also try was having your dog work for his food. Don’t always put it in the bowl. If you serve dry food , take a handful, take the dog in the garden , hold it so it can’t see and toss one piece of food about a metre away, you’ll be amazed to watch the dog quarter the ground until it finds that treat. Working it’s brain will also go a long way to tiring it out.
Good luck !!