The next character that you must meet with is Samuel. If you wait too long with completing this quest then Samuel will give stocks to your opponent. Just like with Robert, here, you must also learn about Samuel's location by meeting with James Berry in the appointed city. He is a criminal that needs you to get him out of the city. Do not offend him - by doing that you can lose a lot of bandits reputation.
You can ask him about the brother or go straight to travel costs. If you want to learn about brother's location you must ask him about that. Otherwise, if he pays you when you reach the destination you will fail the mission (you won't learn where to search for brother). Try to have at least a medium passenger carriage and fill it with passengers. If you see an enemy army patrols on the map you should try to avoid them, even if you have to make a long detour - your carriage can be searched through on outposts. If they find the wanted (or contraband) you can start an unnecessary fight (and lose a lot of reputation). You can also point out the prisoner (which fails the mission).
When you get the prisoner to the target he will tell you where you must search for brother. It would be good if James Barry dies earlier - Samuel will order you to assassinate him. You must acquire 12 jewelry chests that will serve as a bait for the criminal. If you won't have the chests with you then the bandits, that stand near the tracks, will simply ignore you. After the fight you must go back to Samuel and receive stocks (4%). He can also join your team (for free).