Since this story is set 20+ years after the show and is very much LA Tribune: The Next Generation it isn't too important to know too much about most of the original characters, but briefly:
Lou Grant was a CBS show, a drama spinoff from the Mary Tyler Moore comedy show, which ran from September 1977 to September 1982. The background was journalism, the editors and reporters of the Los Angeles Tribune, a major newspaper,. the stories it covered, and the paper's internal politics, business problems, etc. It was one of the first to deal realistically with issues such as school violence, mental illness, labour disputes, and rape.
The main characters were Lou Grant, a crusty journalist and editor of the Los Angele Tribune, Art Donovan his assistant, Charley Hume the managing editor, reporters Joe Rossi, Bille Newman, photographer Dennis Price, AKA Animal, and Mrs. Pynchon, eccentric owner of the paper.
For the purposes of The Rosenberg Inheritance Mrs. Pynchon is now dead and the newspaper is owned by media tycoon David Nabbit, who appeared in episodes of Angel. Grant and Hume have retired, Donovan now edits another paper in San Francisco, and Joe Rossi is now the paper's Foreign News Editor, Billie Newman the City Editor, and Animal the Picture Editor. All of these characters are now in their fifties.
Billie Newman is simply a good reporter, who feels that her competence is more important than her sex. She's red-headed (now greying), attractive, a vegetarian, extremely stubborn, and tends to dig deep for the facts, qualities that have carried over into her role as City Editor for this story. Since the 1980s she's married and divorced twice but has no children, and has kept her maiden name.
In the original series Rossi was played as an aggressively competitive reporter who tried to get stories fast, sometimes sacrificing accuracy for speed. For the purposes of this story he's mellowed a little but still expects quick results. As part of a long streamlining process the paper no longer has a Deputy City Editor; if Billie is ill or on vacation the other journalists share her workload, with Rossi taking over as City Editor and his role on the foreign desk taken by other members of the paper's staff.
Animal is a former hippie, still an excellent photographer although he now spends most of his time working with photographic editing and layout software; the paper has gone over to digital photography for most purposes, and Animal prides himself on being one of the few members of the staff who can still handle every stage of processing and using old-fashioned film when necessary.
Pictures and biographies of the staff and actors can be found on many web sites; the first two or three sites found on a web search for LOU GRANT CHARACTERS contain everything needed for the purposes of this story.
All other LA Tribune staff mentioned in this story have been invented by the author.
A good modern film equivalent of this series is the film The Paper, which covers some of the same issues, although it is more of a comedy than Lou Grant.