DOG HELP!

We took in a two year old pit mix. I’ve raised tons of dogs before and trained them but they were always German Shepards and puppies when I got them. This dog is DIFFICULT! She is driving me INSANE. We have had it for 4-5 months and she refuses to listen. We have three rules. She can’t be in bedrooms, she can’t be on the couch, and no people food. I’ve been trying to train her for months and I thought I was getting somewhere but actually she just waits until we are asleep or I go upstairs or somewhere else, then she’s back on the couch or in our beds. I’m at my wits end. Nothing I’ve tried is working. All she does now is waits for her opportunity to get on the couch or the bed and then she jumps off if she hears me coming. On top of that I’m having a huge problem with her getting on the table and eating our food. I literally walked away from my plate for two mins to use the bathroom and she ATE MY ENTIRE PLATE OF LOBSTER AND CRAB. I come downstairs and it’s all over the floor. My two year old will have snacks in his hand and if I’m not watching the dog she will take the snack right out of his hand and eat it. And my son starts screaming that the dog ate his food. I can’t get rid of her because I took her in for a family and I promised to keep her and keep her safe and I won’t break that promise. But I’m losing my mind. I have to watch her at ALL times or else she’s doing sneaky shit. Idk what to do. Please help.