Quitting the family business (Long)

I work for my family, specifically my maternal grandmother and my aunt. My grandma is very...grumpy. And my aunt is the most selfish, fake, judgemental person I know. Together, they own a furniture store. I've been working for them since they opened in February of 2018. It's MISERABLE.

There is no organization. We have weird hours, so the scheduling is a little tricky. But they'll call me the night before at 11:30pm and ask me if I can be there the next morning at 9:00am. When I am there, I have no idea what I'm doing because there was never any type of training. So when Joe asks me if Console Table A comes in blue, I have no idea. When Sharon asks if Sofa/Love Combo has a matching Armchair, I'm lost. When Michelle wants to know how long the shipping time is on a specific manufacturer, I'm a deer in the headlights...you get the picture. Even the POS system is a labyrinth.

Favoritism is real. I was born to the most incredible mother who would give the shirt off her back for anyone. Her mother, my grandmother/boss, disagrees. She has always had a distaste for my mom. And because of that, an inherent distaste for yours truly. Now, my aunt/other boss has always been the favorite. It's a real issue in the fam; always has been. Okay, now keep up: as well as my aunt and my mother, my grandmother has a third daughter. THAT aunt's daughter also works at the store. So my little cousin. She's 17 years old and the only person they trust enough to train. I don't know why, but for some reason, she's the only employee who can work the computer system, lookup SKU's, order inventory, make sales, etc. Weird, right?

The worst part of all, BY FAR, is the lack of - no - the REFUSAL of ANY sort of communication. This is where things get really nasty. Both my grandma and my aunt avoid confrontation at all costs. On a few seperate occasions, they have reached out to my MOTHER to discuss my performance. I am an adult. If there's an issue, they ought to take that up with me...not tell my mommy on me like we're in the third grade. Here's the real kicker though; I've done NOTHING wrong!!! I am always working, 10 hours a day usually! No breaks aside from a 30min unpaid lunch, always cleaning or decorating or arranging or helping customers (as much as I can with no training anyway). I do EVERYTHING they ask. And all they do is talk shit about me behind my back and to my mom.

So, in conclusion, after working for them for 4 months (3 of which were unpaid btw), I am done. I'm done being treated this way. If I continue to work there, I will forever resent my family. And I don't want that. How do I quit? What do I say? Obviously I'll give my 2 weeks, but I don't know what to say. Or do I just tough it out?

Please note, I've tried time and time again to talk through this. I've confronted them. I've asked for help and training and structure and communication. And all I get is empty promises and blatant disrespect. Today was my breaking point. What do I do?