I know I should respect my elders, but it is getting tough

So everywhere you go, ppl tell you to respect your elders, especially your parents. In Texas, we are huge on respect (if you visit, ppl will call you ma'am, miss or sir almost everywhere) and if you have no respect, you will not last long.
Now with that said, it has been drilled in my head to "speak when you have been spoken to", "if you have nothing nice to say, don't say anything at all", "kill them with kindness" but what do you do when it is your own family that is crossing the line?
I have been off my meds for a while now, and I have found a few ways to calm myself down and can pretty much handle any stressful situation. I know I have debt, I know I have things that need to be done now, but I also know I can only do so much right now-the rest is out of my hands- and there is no point in stressing so when I am out and about, I am generally happy, but when I get home, it is like entering a war zone! You can imagine with our sensitive stomach how horrible that can be, especially when you know that is what you have to deal with daily.
I can start with my grandparents. I love them, but sometimes they do not know what is right and what is wrong, it is not my place to tell them either. Let's just say there has been some abuse to and from them to each other and their kids. One party is scared of course to say anything, and usually keeps quiet, but says insulting things without thinking about it. Now, again I love them, and that was just how they were raised, so I watch what I say and do around them and just keep going on with my day. My mom, growing up with that, it rubbed off on her. She is basically a child in a grown up persona;she cannot express her feelings in the right way. She has never beaten me, but there is some verbal abuse that I do not think she realizes is coming out. She is never satisfied, always negative and likes to push buttons. I have always tried to make her proud and it is just now dawning on me that that is an impossible goal. I had some ppl close to me notice her behavior and they don't understand why I didn't notice it earlier. Mind you, she is married (to man that is not my cup of tea but whatever), he buys her EVERYTHING! We have a nice house, the newest of every technology available, she has 2! of her dream car and she has her dream dog. Since I am sick, it can be hard for me to clean when she wants especially when I have work that day. I get exhausted and something just gross me out, she flips out! I have a cat, and cats sometimes like to mark their territory or pee everywhere and it is pretty hard to get the smell out, I clean it, but it has to be repeatedly cleaned to fully get everything out and even if I do keep cleaning she complains it smells but it can never be her dog, even tho the dog is old and sometimes takes relief on the carpet. Anyway, the point is she is negative and she is the only stresser I have that keeps getting worse! My sisters don't understand either and my dad chooses to ignore it. I am basically dealing on my own except for the few lucky friends I have acquired.
I literally need antidepressants for living in this house, and not to go on a rant, but my step dad isnt any better. They will say any and everything to push your buttons. I will admit, I tease ppl but never with the intent to hurt their feelings. I just need help.