I now have a huge pile of things generic to each enemy that now just handle themselves without having a million different sprites about.
For anyone else, basically I do:
On enemyfamily create -> Spawn healthbar
Spawn other things
Set healthbar ID to enemy.UID
I then do a for each healthbar with
enemyfamilypick instance with UID healthbar ID
Works great and means that my event sheet is a lot smaller as is the list of objects in my project.