Re: Federation members or not? (Canon sources only, please)
Memory Alpha claims all four planets are Federation members. The most doubtful of these claims (to me) seems to be Benzar. MA says Benzar became a member in 2378, which would be during Voyager's final season, but their source for this is Star Trek: Star Charts, not a specific episode.
Dr. Howard, Dr. Fine, Dr. Howard: For duty and humanity! --Men in Black (1934)