Oh, I know what you mean. I got 2 solutions. First requires one hp bar for each different kind of enemies. The second is one hp bar for all enemies.
1. Make your enemy, make your hpbar. Click on the enemy, left is your properties bar, seek for the container option and add the hp bar for it.
If you spawn your enemy, the hpbar will spawn also, linked tot he enemy.
Make a private variable "hp". And then:
"condition when player hits enemy:
subtract 'value' from enemy('hp')
set hpbar.width to (100/enemy_max_hp) * enemy('hp')"
Replace the 100 for the with of the hpbar.
2. I'm not sure with that one. I would try a "for each" loop.
For each family(enemy):
condition when player hits enemy:
set hpbar.width to the private variable 'hp' of the family, again like in step one, with the rule of three.
But I'm not very sure with this one^^. Someone has to reply/improve/add this one, so that it's right
ps: I'm not one of the advanced users here, this the way I would do it, maybe someone else has better solutions :)