In the screenshot above, the bars indicate the health and 22/42 is the percentage of health. The other numbers to the right of the bars, 76% and 66%, indicate your threat relative to each mini boss's current tank.
IN ORDER FOR THIS TO WORK PROPERLY, YOU NEED SOMEONE WITH THIS WEAK AURA ON BOTH SIDES.
This aura can only calculate the health and threat for your current target, and it will sent it to other people using this weak aura. If no one on the other boss is using the weak aura, you will not get health/threat updates.