Families are great for grouping objects to simplify code, however they do create some issues when trying to pick particular objects and referencing instance variables etc.
https://www.scirra.com/tutorials/556/understanding-picking-with-respect-to-families
But, used properly you can use them to optimize your code quite a bit. Basically they group objects so you can do things like hit check against all objects in the family "monsters" versus checking against Troll, then Archer, then Grue, etc etc.
Thanks for the info, what would you suggest when i want to multiply my enemies, what should i do first?