Since it's a novel about the gods of tango, the main characters could be the ones who are at the forefront of the tango movement. They might be those who are changing the way tango is performed or perceived. It could be a group of friends or rivals all vying for the top spot in the tango world, each with their own unique style and story.
I don't know as I haven't read the novel. It could be tango dancers, instructors or people who are really passionate about tango.