Half pit, 1/4 rott, 1/4 pyrenees???
That sounds like a nightmare to me. I have experience with all three breeds and if you think the Pyrenees if going to mellow out the other two, you are mistaken. Pyrenees are among the most ferocious beasts pound for pound on the planet. They are fearless and don't domesticate very well. They are still a true working dog.
Good luck on that dog and don't tell your insurance company because they'll probably cancel you.
Both parents had good temperaments and he hasn't shown the slightest bit of aggression at two years old. My last dog was a Cane Corso Mastiff which is a large breed that can be a handful. I just put him down at 11 years old because of health reasons, he was the best dog I ever owned by far. I didn't get another one because I didn't like the fact that the breeds popularity exploded and there were too many bad breeders.