¿K?

Watching Narcos on Netflix.  Weirdly, Pablo Escobar addresses his brother as usted, while his brother addresses Pablo as tu.  Can this possibly be Colombian usage? I find it hard in any case to believe that one brother would address another as usted, but if this sort of asymmetry were to occur, I would expect the more powerful to use tu and the less powerful to use usted. Baffled.