Did Richard suffer from a mental disorder?

It might not have been stated explicitly but I have a theory. I do think that Richie suffered from either schizoaffective disorder or schizophrenia itself. I'm basing this on the paranoid delusions that appear to plague him through out the movie. I do think that director Robert Rodriquez left this open for discussion intentionally. It is certainly one of Richie's many character flaws. The fact that he burned down the house and in doing so killing their abusive alcoholic father should have been a red flag. So is Seth aware and choosing to ignore his brother's disturbing behavior? Probably. It may explain why Seth repeats his mantra that Richie will be fine once they arrive in Mexico and reach El Rey. Another couple of examples that come to mind is the shoot out at Benny's World of Liquor and the hostage in the motel room later. Was Pete, the clerk, giving Texas Ranger Earl McGraw signals or was that all in Richie's head? Clearly the terrified hostages are human yet Richard tells Seth they were demons messing with his head. We see the same thing with the hostage who winds up dead after Seth leaves her alone with his brother. Once they reach The Titty Twister Richie's psychopathic personality appears to resurface as he beats up the doorman with glee. Earlier in the RV he tells Seth that they should shoot the Fuller family because they are demons. Something that Seth brushes off.