Hit points are not part of PC knowledge.
There is no mystical Heal skill that imparts knowledge to the PCs that another PC has failed two Death Saving Throws.
There is a non-mystical heal skill though. Although it seems that your point is that is is NOT within a players insight or perception to know which of 2 people they can see IC is worse off. I would be pressed to believe that if I was playing a field medic class (leader). Although, why would a player know if they made the death saves? Or how much hp they have left? You want to add drama, don't let players roll their own death saves, roll them hidden and tell them when they go from needing a cleric to needing a grave. Better yet, don't. Just have them be surprise when someone tries to heal the corpse and fails.
Also, I disagree that being able to tell that one person is more bloodied then another is more gamist then having fixed states of health. Also, in your statment of "This character has 3 and this has 5 left" they are BOTH horrible off. The distinction is not terribly necessary. If it were 5 hp and oh 40 cause it's high epic, they are both bloodied, but one is way more injured. This should be noticable.