I only refer to Frank as "he" because that is the way he is still gendered in the movie, if I'm remembering correctly. But "they" does feel more accurate. Oddly enough, Richard O'Brien (writer and Riff Raff) is super duper transphobic and doesn't consider transwomen to actually be women. Yet, they've also mentioned that they consider THEM SELF non-binary, so they're totally cool with a third gender as long as it extends to them and them only.
Frank definitely has something about him that lures so many people in. According to Columbia she was just someone on the street that Frank found and lured her in, and then got Eddie in, and then despite how much Brad and Janet hate being there, there's still something that attracts them. But, also, I definitely think they are all villains in this story. No one except maybe Rocky comes out really clean in this story. Even with Brad and Janet being victims of stumbling across this castle in the night, they are total assholes (ASSHOLE!) and I don't exactly *root* for them throughout the story.