About the mafia
The Mercer Family - named after its first (and greatest until now) boss - is a mafia that uses a cabaret club as a front while dealing with the shady business behind the curtain.
People do not know, though, that Amaranthine, the cabaret club, is owned by the Mercer Family, so that it won't get attacked. This means that even the cabaret girls and boys and the staff working there don't know about it and think it is just a normal club. Although they work for a mafia the mobsters treat them well and don't exploit them - the soldiers even act as security for the club and protect the girls and boys from any harm.
So, don't mess with our girls and boys or you'll be sorry, mate.
The atmosphere in the family itself may be more on the mature side and there will probably be MRP (don't confuse it with ERP!) but they aren't all dark and gloomy - and neither totally evil. Yeah, they are criminal and deal in shady business like smuggling, selling drugs, extortion, hits (not music - like hitmen) and so on but they wouldn't rob poor people or those with a shitty life. They want to follow Mercer's example and be more like a "gentlemen (females can join, too, of course) mafia" that could still mess you up if you cross their way.
The current boss of the mafia is Yitani although her own mobsters don't know that. She has two sides to her - just like the family itself.
For once, she is the manager and lead cabaret girl (she even works as a cabaret girl herself) of Amaranthine and acts like a sweet innocent woman in public with a little side of doofus sometimes.
She also is, on the other hand, Whitevine - the leader of the Mercer mafia - who's face is unknown because she always wears a mask with an integrated voice changer and acts completely different from her other self. Only her closest high-ranking subjects, like her sister and cousin, know that Whitevine is not only the mafia boss but also the manager of Amaranthine (please don't metagame by your character knowing that - they only know this if I allowed it).
Members of the mafia should wear a suit while they act as mafioso - anything else would break immersion, after all.
Preferrably white ones like the big Xaela in front of the entrance has (just the normal white that you can buy with gil). There is usually white dye in shelf 2 of the company chest, so just ask a higher-up or senior cabaret girl/boy to give you some.
A closer look at the family's ranks
The ranks should be quite easy to understand but here is a rundown of them:
Obviously the one in charge of everything and the one the rest of the family follows. Every new member has to swear their loyalty to the boss, which would be Whitevine in this case (Yitani's other identity). If they do break this oath a terrible punishment will await them, so don't try to betray the family.
The second in command after the boss and the one that takes over when Whitevine isn't around. There is only one and you should treat her with the same respect as the boss.
The brain of the family and the one that is usually consulted when big plans are scheduled. Can take over if neither the boss nor the underboss are around but doesn't have all privileges like the bosses do. There is usually one but who knows - if the family becomes big enough there could be room for another one.
Acts as an officer and leads soldiers during coups or other kinds of maneuvers. Needs to have good judgement and reliability - it is a leadership position, after all. Soldiers have to listen to them and they act as management staff when they work in the club - they organize the cabaret girls and boys (when the manager isn't doing it or in a session herself), greet customers and inform them about what they need to know and show them to their booths before calling for the cabaret girl or boy that was ordered. They do not bring food and drinks, though. That's what housekeeping is for. Of course, not every capo has to do this because you don't even need so much management staff during opening hours.
The normal rank and therefore the one that most mobsters will have. They are the backbone of the family and act as its "army" while being led by capos or higher-ranking members. They are not newbies anymore, though, and are expected to pull their weight.
When they work in the club during opening hours they act as security and watch out that all customers behave - they shouldn't just punch away, though, and are expected to handle unpleasant customers with care. They are there to protect the girls/boys and warn - or throw them out when they ignore the warnings - misbehaving customers. Not every soldier has to do this, though.
Is on the same level as soldier and just a second type of normal member. Instead of joining coups and other maneuvers they usually don't fight and instead do other handywork.
Like dealing, getting supplies, mending and mechanical work (like maintaining the families airships), reeling in information and so on. They may not be great fighters but they are clever enough to make up for that.
When it comes to the club they have not set tasks and can usually decide by themselves if and in what way they want to help - although one of them could sit behind the counter and take care of the paper work. They could even fill in for management staff when it comes to greeting customers.
A new blood and someone who joined the family recently. Has almost no privileges and shouldn't expect the others to take them seriously. Also does most of the dirty work that others don't want to do but is not allowed to accompany the family during coups. If you want to become a full member you will have to prove your worth - how your trial to become a soldier will look like can vary and the capos are usually the ones organizing them after receiving confirmation from the boss.
Can substitute for housekeeping when the club is short on staff for opening hours.