Susan,
A small clarification: ?If the "We have several subgroups for committee work and they have members who are staff"?subgroups are part of the "residents have created a group for resident communication only (no staff can join)."?main group, the "no staff can join" statement is incorrect; they are already members of the main group because subgroup members have to be members of the main group. ?So in all reality, everyone (residents and staff) is a member of the main group, it's just that some are members of one or more subgroups, depending on whether they are staff, residents or whatnot.
Cheers,
Christos
Christos Psarras