can u get this armor without killing one of them for the armor

No. If you have a PC you can cheat and enter the console code for it, or ive heard you can sneak behind them and give them a better armor piece or plant a nade in their pocket and fast travel away really quickly. This kills them but you dont get negative NCR rep points if done correctly.

You could reverse pick pocket for it. But you'd need power armor.

I'm guessing, I just kill one of them.