Taking down Sal Marcano requires a lot of resources and manpower. You can't do this alone so you'll need the help of three major crime bosses that can help you with your cause. These figures have issues with Marcano himself and won't stop at anything to get back at him.
Leader of the Haitian Mob, she runs a voodoo shop in the Hollows. Nothing is known about her except that she started her operations in the Hollow. You'll first get to know the Haitian Mob after learning from Sammy that your family's lottery operations are being robbed by the members of these migrants. The funny thing is that everyone thought Baka is the leader of the mob. So how does a woman build a criminal organization while keeping her identity completely hidden? No one knows except Cassandra. Under her effective leadership, the Haitian gang becomes the first major force that Lincoln has to tap on to get the initial muscle and resources for his next moves. Make no mistake however, since Cassandra can be quite unpredictable so thread carefully when dealing with her.
Vito was a rising star in the criminal underworld of Empire Bay. See these unfold during the events of the preceding game of the series, Mafia 2. He was a WW2 veteran who got himself a jail sentence shortly after coming home due to some jobs he pulled off. While serving time, it's when he met the Vinci family consigliere, Leo Galante. This started his long, complicated journey in organized crime. Vito is responsible for greasing Don Carlo Falcone, Empire Bay's mob head. However, even when he's protected, he can't stay so he was "banished" to New Bordeaux and became Sal's problem. Sal didn't like him from the start. He assigns the River Row district to him. Vito's loyal and can be a very sympathetic ally but he's definitely a killer. He'll come after you if he thinks you're planning to f**k him.
He's the leader of the Irish Mob and really loves his booze and degenerate lifestyle. However, you don't want to be in the end of his rifle. He runs a "legit" garage/ vehicle compound where he salvages parts from stolen vehicles and sells them for profit. He also take part in bootlegging, truck boosting, and narcotics to name a few. He lived most of his life in New Bordeaux, although he considers Belfast as his true home. In an attempt to bolster his rep, Burke f**ks up a big shipment of stolen car parts. Marcano sends the Butcher which in turns messes one of Burke's legs while also taking away control of his assigned district, Pointe Verdun.
These are your underbosses' right-hand men. If something goes wrong and the underboss gets killed, they will take over and continue operations. (though they don't get promoted) They have their own brief backstories but aside from a few conversation/ story missions, they won't have any lasting effect in the game's narrative.
A Haitian exile and Cassandra's second-in-command. He handles Cassandra's weed operations. He helped smuggle people trying to escape the murderous secret police under Papa Doc Duvalier and somehow ended up in the Haitian gang where he also serves as Cassandra's religious advisor, even if he's not really connected to voodoo.
A Cuban expatriate who is formerly part of the Anti-Castro Movement, she now handles Vito's smuggling operations. She can smuggle items in and out of Cuba without the coast guard or navy even getting wind of it. Donovan describes her as "half-pirate".
Burke's only daughter and also in the "cleaner" side of the spectrum. Lincoln and her go way back, with young Danny in tow. Now, she manages the bootlegging operations in the Irish Mob. After Danny's death, her existing spat with her father only became broader. She wishes to leave New Bordeaux when she gets the chance.
Associates are tied to your underbosses and each of them provides much needed backup services that will help you in your various tasks. There are associates that provide their services free of charge while the others require a considerable amount of money as payment, in exchange for more risky and high-end services. These services are also further improved when you increase the earnings of the underboss they're associated with. You can access the associates in your weapon wheel. For more details for each associate, refer to the individual list of favors per underboss as listed in the dedicated section of this guide.
These missions are ugly ones and will require you to kill one of your underbosses. This will happen if you continue to ignore an underboss during sitdowns. You can also make them very mad if you assign them a racket in the district, only to assign the district to another underboss. Another reason that can make them rebel against you and quit the team is when you unfairly assign the districts between them. There are nine districts you can assign to your three underbosses. If one of them gets unfairly ignored, it will trigger a walkout and a succeeding betrayal mission.
During a betrayal mission, you'll be tasked to infiltrate the renegade underboss' hideout to kill him/her. Once done, the underboss' lieutenants will take over and will continue their pending optional missions.