Sans has more than 1 HP! As you know if you check sans in his battle it says that he has 1 HP and because he can dodge it makes him strong. But in the hotel in Snowdin if you talk to the baby bunny he saids that sleeping can make your HP Go higher than your Max HP. Sans sleeps a lot!

Why is Sans the only one who bleeds?

Well Sans bleeds when we hit him. It affects his physical apperance. I know its his physical apperance because when Toriel dies (or anyone else im just using her as an example) her soul shows, revealing that the battle sprites are them and not just their soul . So this would mean Sans has human soul.

Does Sans have a human soul?

Sans has no soul so it wouldnt appear when Asriel broke the barrier.