Which ones were 'the Brat Pack'?

All of them were lumped into that group except Mare Winningham.
Demi, Andrew, and Rob were also mentioned in that article that started the whole Brat Pack.

Knock if off Napolean make yourself a dang quesadil-la!

The term was coined inNew York Magazine profile article and referred to specific actors.

Then the term entered the popular culture.

The original New York magazine article listed eight actors as being members of the Brat Pack:

Emilio Estevez
Judd Nelson
Rob Lowe
Tom Cruise
Sean Penn
Nicolas Cage
Matt Dillon
Timothy Hutton

There were no female members. Anthony Michael Hall wasn't a member of the pack. Neither was Andrew McCarthy.

Emilio Estevez
Anthony Michael Hall
Rob Lowe
Andrew McCarthy
Demi Moore
Judd Nelson
Molly Ringwald
Ally Sheedy.

^Those are the "official" core members of the Brat Pack. Most of the other young performers mentioned in the original article were more or less considered "Brats by Association". James Spader should be in there as does someone like William Zabka if only because either of them always played the antagonist in most of the 80s teen movies. Mare Winningham is counted out mainly because she not only just appeared in St. Elmo's but was also like Alan Ruck from Ferris Bueller, several years older than the core "brats".

Theres a couple of books on the subject: Pretty in Pink- The Golden Age of Teen Movies, and You Couldn't Ignore Me if You Tried.

Both go in great detail on the whole Brat Pack phenom of the 1980s.

When theres no more room in Hollywood, remakes shall walk the Earth.

It depends on if you go by the list that the author of the NY magazine made up or if you go by the idea in popular culture of the group of actors from the 2 main movies- Breakfast Club and St Elmos Fire. Many of the actors considered Brat Packers were only associated with the name as "cousins" of the core group.

Emilio Estevez
Judd Nelson
Rob Lowe
Ally Sheedy
Andrew McCarthy
Demi Moore
Anthony Michael Hall
Molly Ringwald

were all in the 2 main movies but there were some others cited as being in the group according to the article and its author- Tim Hutton, Sean Penn, Clayton Rohner. Many people associate other names in the Pack if they starred with the core group- saying Robert Downey Jr bc he starred with Molly Ringwald or James Spader bc he starred with Andrew McCarthy. It's sort of like 6 degrees of Brat Pack. The article's author had gone out to eat with Emilio Estevez, Judd Nelson and Rob Lowe so they were kind of the core core group and of those 3 only 2- Emilio and Judd starred in both core Brat Pack movies. (interesting cultural phenomenon)

The most commonly cited members of the Brat Pack include Emilio Estevez, Anthony Michael Hall, Rob Lowe, Andrew McCarthy, Demi Moore, Judd Nelson, Molly Ringwald, and Ally Sheedy. The initial New York Magazine article covered a group of actors. Most of the cast members of "The Outsiders" were mentioned including Tom Cruise, C. Thomas Howell, Matt Dillon, Patrick Swayze, and Ralph Macchio. Charlie Sheen appears in several lists – more for his family relationship to Brat Pack leader Emilio Estevez and his partying than for his collaborative film work with other members. James Spader and Robert Downey, Jr. have also been considered members, and performed alongside other Brat Packers: both of them with Andrew McCarthy in "Less Than Zero", and Downey with Anthony Michael Hall ("Weird Science" and "Johnny Be Good") and Molly Ringwald ("The Pick-up Artist"). Other actors who have been linked with the group include Kevin Bacon, Matthew Broderick, Jon Cryer, John Cusack, Corey Feldman, Jami Gertz, Corey Haim, Mary Stuart Masterson, Sean Penn, Lou Diamond Phillips, Kiefer Sutherland, and Lea Thompson.