Quick Question

So this is my first fallout game and I absolutely love it. However I am trying to do all the quests simultaneously for as long as I can before having to pick a side and keep my allegiances there. However several times I have encountered, in the wasteland, two or three of the factions just having a random battle royal. No raiders, usually synths vs my supply lines or some brotherhood of steel guys. One time near a town (I forget which) all of the factions I had become a part of had a MASSIVE war (granted this was during a quest to retrieve something or other) but I had no problem just walking through the whole battle without taking a single shot because they were just fighting each other and seemed oblivious I was even there.

If I step in and kill a synth or a BoS member will that faction turn on me right then and there? what is the deal here?

Please avoid spoilers if at all possible

TY