Google (email) Groups are built with their constituent (sub)groups and a small number of individuals (the fewer the better). Those constituent (sub)groups are made up of individual members.
One example:
All CERSD (top level)
ES Staff
ES Certificated
ES teachers, other certificated employees
ES Classified
ES paras, other classified employees
Individuals associated with the ES but not in any other ES Staff subgroup (custodians, nurses, etc)
Best practice: Manage (add/remove) members at the subgroup level, rather than at the top level. The higher levels should have minimal individual members. From the top level down, simplicity is key.