Basically families are like groups of same objects type (families of sprites, families of text objects etc).
If you create a family for sprite objects (not sure if there's a limit of attached objects) you can then set a variable for your family (not sprite but family itself) and all members of that family will inherit this variables.
Create Family - "my_objects" with family members: sprite1, sprite2, sprite3, sprite4
Set family number variable "health" = 0
this means that every member of family "my_object" will have number variable called "health" = 0.
And here comes the best part. You can set this variable independently for each member and they will keep track of it's own value.
Sprite1.health = 2
Sprite3.health = 4
If you set your actions to something like:
+On left mouse button clicked on "my_objects" - > subtract 1 from "health"
then if you clicked on Sprite1, -1 will be subtracted only from this object.
Same goes with behaviors.
Families, containers and functions are your best friends :D