I have a very close friend who had a pit. Her and her bf, had the dog from a puppy, raised him in a family with 2 young toddlers, and a older child. This dog was spoiled just like any boxer on this site. I saw this dog almost daily on visits, and was friendly to EVERYONE. At the age of 3-4 for some reason he just started acting strange, similar to your friends. Plus he was neutered. My friends father would come to visit, who the dog knew very well, and would often go on walks with, suddenly became defensive to, its was very odd. They spent thousands at the vets, and on behaviourlists trying to figure out what happened to there baby, but all got no answers, besides advise to put him down, because of the breed. Of course they wanted nothing to do with that, and kept working with him, because after all they didn't believe in the pitbull reputation, and this was there first baby. After a few months of this, and no success, the dog almost killed a friends child, and attacked its owner, who was trying to remove him from the baby. It was a very sad ending for both dog, and child, who is scarred for life, and of course the dog was put down.
This is just one of the stories. I have had several friends with pits as pets, and friends who of course know others who have had them. Personally I don't say anything negative about them, because I personally have never owned one, but to be honest, never will. Some people are fine, and they have a happy life together, my husband has a friend who ownes one, and him and his wife have a young baby, and we see them walking with the dog attatched to the stroller!! You just never know.
I wish your friend the best, and hopefully this will be sorted out for not only there best interest, but the dogs as well.