I seem to be in the minority in my reactions to your follow ups OP, but I will post what I think anyway--maybe just to give you some alternate perspectives to think about.
My son is find doing what he's doing for now. We had cut him off financially unless he went back to school, learned a trade or made some serious plans that involved his future. And even then we'd only offer minimal support. I know it seems like the issue seems like it's about my son but it's not really. Imagine you did lots of things for a family member and went them and asked them to do you one favor. They responded by doing the exact opposite in order to benefit themselves.
I really do not feel it is appropriate to ask a "favour" which involves asking someone to not help out or hire another adult. It was not your business to get involved in what was happening in your adult son's life int that way and it would have been inappropriate for her to change the offer she made your son because you did not want that for him.
If your son is fine with the situation, why are you so upset about this? You cut him off financially (completely understandable) and he found work and housing that allows him to build skills in a trade he is interested in. I REALLY do not see where there is a problem in this at all
Overall the experience has been good for my son. Not economically but in terms of confidence. He completely opened that restaurant, creating the menu, establishing relationships with vendors he chose hiring staff... And he runs the place. That's why he works so much. But there is no money to pay him a fair hourly wage. It's a new place and sister went broke opening it. He is not making anything close to a beginning chef's wage. But he still doesn't want to go into restaurant work permanently. This is just a way to stall making decisions.
I didn't cut him off because he went out there. And he had everything he needed. I just was trying to make it a bit less appealing to flounder. I wanted him to get tired of not having nice stuff. My sister may not be paying him a bunch but she bought him a nice used car, takes him to show and gets him into clubs and busy him fancy clothes through connections she has. She has many connections and can get him things that I couldn't. Unfortunately, these things are tempting to my son right now. She is not doing it for her kids unless it's to reward them going to school. This is one of the reasons I asked her not to lure him out there. I told her if he didn't want to cook I wanted it to be hard for him to continue to make foolish decisions.
Okay, so he is "Stalling" making decisions. So what? In the meantime he is able to live without sponging off of you. He is working hard--not couch surfing while playing video games all day or using drugs--WORKING. And, it sounds like he is gaining valuable business skills and experience, that even if he ultimately decides not to pursue restaurant work as a career, will be helpful to him in life and other careers.
He is not making much of an "hourly wage" Is he paid hourly right now? Or salary? It is expected that in a start up business, the main manager or owner will put in very loooooooooong hours and often that works out to a salary that equals very low HOURLY pay. It also sounds like your sister has been able to "supplement" that pay by offering him housing, clothing and entrance into clubs. As a man in his young 20s who is "tempted" by those things, it is liekly that if he were making more money right now in a different situation, he would be spending most of that on rent, designer clothes and clubbing--so at the end of the day it is likely not much difference.
It sounds to me like your son and his aunt have worked out a reasonable arrangement which they are both comfortable with (you said yourself he is fine with it). He is working. He is gaining skills. All of his needs (food, shelter) and many of his wants (clothes, clubs) are covered by his "salary" and the side benefits she offers him.
From what I can tell, you are upset because this is not the path YOU wanted him to take in life and this is not the place YOU want him to be right now. However, HE is fine with it and this is where HE wants to be at the moment (and it IS something productive). You are angry with your sister for giving your adult son the opportunity to follow this path and not making it difficult for him to stray from a path you would have preferred.
From what I can tell, it seems YOU are the one who quit speaking to her over this and now you want her to call and make it better?
Based solely on what is posted here, I think you want to be overly controlling of your son's life and are angry at her for not enabling you to do so.
I really do hope you can move past it and make enough peace to have family gatherings--for the sake of the rest of your family.