Pics of the dogs here...
That second one doesn’t look like a pit mix to me, FWIW.
You can not tell the lineage of an animal just by looks. They can be mix pit and still look like a hound dog. I can attest to that about strays that I have encountered that I befriended only to see their behavior displayed later on as a typical terrier act. I have an elderly 15 year old mix that you would never guess she had Chow mixed in her blood except that she has a black tongue. So no, you can not tell just by looking at them.
Irrelevant. You can bet the pit was the instigator. And the truly aggressive one. It definitely has the more serious bite.