My logic would be that Simon would vote Bernie as he feels he is the most intellectual, Theodore would vote Hillary as she's the most motherly, and Alvin would vote himself because he is, for the lack of a better word, an egomaniac.
And for the record, Jon Arbuckle would vote Hillary to impress the ladies.
This is an interesting point of view and I understand your angle. This is very important so I'll try to be thorough here. Please stop me if you have any questions.
I believe Simon would vote for Hillary because I consider him most likely to have been political for the longest of the three brothers. He is definitively liberal, but I think he is a moderate economic. He agrees with lots of Bernie's ideas, but is not confident in his ability to realize them. Bernie's singular messaging also leaves Simon wanting. Foreign policy is important to Simon and believes we need a world leader, not just a president.
Theodore would vote for Bernie because he thinks he is the "nicest." He likes Bernie's environmentalism and the idea that he is always looking out for the disadvantaged. But Teddy thinks smaller than Simon and doesn't know much about how politics work. Theodore is sort of a classic first-time voter who doesn't know much about how the game is played, he just wants a nice person to be president. This is honest, but problematic.
Alvin doesn't know anything about politics. He thinks both parties are the same and that all politicians are corrupt. He identifies as a libertarian because it's a convenient label for his lazy apolitical POV that only comes out once every for years. He would tell everyone he's voting for Johnson because he thinks its edgy to protest vote, but he wouldn't really know anything about him and wouldn't actually go to vote. He would tell everyone he did, but he would spend November 8th playing Forza.
It might help if we roleplay this? Maybe we'll be able to find a more clear conclusion if we explore the characters in more personally. PM if you want to meet up.