The Council of Five are a group of five alien races that protect humans against less-peaceful races.
Technically, kids, those are species, not races.
Also, are the council members entire species, or just individual representatives of those species?
Also, alien shouldn’t be capitalized; it’s a common noun, not a proper one. (Humans isn’t normally capitalized, either, although some SF writers do so.)
Also, this example sounds clunky because of the word races (or species, if you fix that) being used twice where they are.
Try this instead: Members of several alien species make up the Council of Five, which protects humans against less-peaceful species. Not perfect, but better.