I listened to a speaker on personal safety one time who made the astute observation that humans are the only animals that deliberately ignore their instincts and teach their children to ignore their instincts. We get so wrapped up in politeness and not wanting to hurt feelings that we ignore our instincts - the ones meant to save us from danger. We see groups of people hanging out on the street who strike us as being potentially dangerous but we don't cross the street because we don't want to appear rude. Our children don't want to hug wierd Uncle Joe because he gives them the creeps and we tell them to hug him anyway. I could be wrong but I sense that you are more than a little uncomfortable about this situation. And it doesn't seem like your BIL is making any concessions. Is his Pit Bull so special that his genes really need to be added to the pool?
And here is a prophetic coincidence: This morning after my earlier posts, I visited with a friend who told me that she and her husband were going somewhere when they spotted a man walking a pretty dog that looked vaguely familiar to her. (She had only seen a photograph of our basenji). She stopped and introducted herself to the man and asked about the dog. He told her that his dog was a basenji (probably purebred) and had been recently rescued from the local humane society just hours before being euthanized. The dog, who bears numerous scars and is recovering from malnutrition, had been used as a bait dog to train pit bulls for fighting! When the pit bull owners got wind that there was going to be a raid, they took off and left the basenji to fend for itself.
To hear this anecdote today just seemed so coincidental. A puppy is just no match to a pit bull. I'm not maligning the breed. I just don't think this sounds safe.
Whatever you decide, we all hope everything turns out well for you and your pup.
Pat