breathing will not change the time line. Such small things as that would have no effect as long as those people didn't draw attention to themselfs and they just blended in then people would've carried on with their normal life's and nothing in the timeline would be changed.
I doubt it, people just being present has an affect on others. If you are walking through a crowd and someone simply sees you and is like "Damn that guy hs some nice long hair" that thought could change his life. He is now going to grow his hair out to be like you. Of course that is an exaggeration but I am sure you get what I mean. Every action has an equal and opposite reaction, meaning if you step on an ant that colony might not survive then an ant eater might die and then that southern hick might not have a dinner.