Having done a couple of 3 and 4 player games.
For 3 players, I've found one of the better, and more fair ways to handle it, is to put a single objective for everyone to go after. Instead of doing different objectives for each person. So, like, everyone is going for one specific treasure item they need to claim. Or everyone is trying to hold onto one area.
While team ups can still happen, the fact of the matter is that no one can really ally. you don't end up in a situation where Lady J wants to assassinate Victoria. Victoria wants to claim the treasure. Then Ramos jumps in wanting to wipe out Victoria or Lady J (something where it easily turns into allies). The team ups may happen, but so will back stabbing.
For four player games. Well, for one you really want to increase the table size so everyone has room to play/move. Two, I highly recommend doing teams. Alliances will form anyhow, and starting with them means you can just do the normal objectives/initiative flow. Essentially you just have 2 teams going, like a normal game. Only, those teams are played by 2 players each.
