I'm so glad to hear you say you know this has nothing to do with testosterone and everything to do with training. I just hate it when I see people being told neutering is a magic fix-all, as I know I was years ago.
OK then, onward.
If cops go to the breeders home for training, can you go too? This is a big dog. You cannot, cannot, cannot have him jumping on people. He will hurt someone, he will frighten someone and you can get into an awful lot of trouble.
In my case I could not have a 70 lb Lab jumping on my then 90 (now 94
) year old mother. All of those other methods you hear about, like be a tree; look at the sky; reward for sitting; no pets from the other person till he sits; they didn't work and he was getting bigger and bigger. And of course Grandma is one of his favourite people in the whole world and she didn't help matter with her actions.
Here's what one trainer showed our whole class for jumping. I call it the Yank 'Em Down method. It's a bit rough. Pup on flat collar on leash. You need a helper. Helper encourages pup to jump on them. When he does you yank him down and use your word for not jumping. That's it.
The little poodle mix understood in one go and no matter how hard the other person encouraged he would not jump again. The other lab took two yanks, my boy took three.
One nice thing about this is that it thwarts all those other people you meet who unwittingly or on purpose get your dog to jump. It's a bit rough, as I said, and if you worry about judging properly how hard to yank and worry about risking injury then don't do it. With mastiff blood in there I suspect you might not have this worry and indeed might lack the strength needed. Depends how big and strong he is.
As for the nipping, my guy got to 6 months and just didn't anymore. One day we were playing and I realized, HEy, he's not mouthing me. I guess it took months of avoiding teeth, chastising teeth, and re=drecting and he finally got it.
Good luck. Post pictures.