Yann Typecasting ? Thanks for this one, I was still calling a custom function with familyObject.UID, and then selecting the specificObject by its UID in the function.
PS : As I didn't understand right away, I made it as an example in attachment.
Blue and Black are in the family "movable", Red is not.
Blue has a "speed" variable, and black has "hp". On collision, depending on the object colliding, the corresponding action will be called.