I think I understand what you want. Since I've never tried to do PvP with my wife (on the rare occasions she was playing with me) I'm afraid I can't answer your question.

To my best knowledge it all depends on what armor you've donned and what food you ate. If both ate the best food and have the best armor and weapons for their biome they're currently in, I'll wager it'll take a few hits to kill the other player. But not too many.