I have seen the fandom sharing clips of Maggie telling Negan that aside from Hershel, Negan is the only family she has left.  ... what happened to everyone else?  This show is 5 years after Rick returns to Alexandria. Maggie doesn't consider any of those people (even Judith & RJ?) "family" or are they all gone?

Yup.  Very confusing.  It seems Maggie was not aware of any of the goings-on in Alexandria, which pretty much contradicts the notion that they had been rebuilding communication amongst communities during that time, and that society had improved to a certain extent.  I guess not so much?