I know people don't talk about this much, but I think that Leopold Strauss is one of the most loyal gang members in the Gang, Here's why:
In chapter 6, in the last mission of Strauss, Leopold is kicked out the camp by Arthur, and he gives Strauss some money to get a job.
It is latter revealed by Charles, in the Epilogue Part 1 that Strauss has been found by the Pinkertons and they tortured and killed him but he didn't talk. By this you can understand how he was loyal to the Gang and how much he cared about them.
Now, I am not saying that he was a good person, but I am saying that he's been a very loyal gang member, even if Arthur kicked him out badly.
And now the Theory
Micah was a rat since the begininnig of the game, here's why:
The Blackwater Heist was planned by Dutch and Micah, and it was a trap by the Pinkertons. Micah was arrested in Strawberry, but the Pinkertons couldn't help him since the gang would've understand that he was a rat. In his camp, Micah has a wanted poster of Dutch, suggesting that he was thinking about giving Dutch to the law and obtain the money. The heist in Saint Denis was also a trap, but Micah talked about the distraction of Hosea and Abigail so Hosea would die and Micah become the co-leader, along side with Dutch. After they got back from Guarma, Micah told the Pinkertons where the gang was so they could've kill 'em. Micah later tried to tell that Bill was the one who was followed by the Agents. Micah even tried to tell that Arthur was the rat.
