Something I forgot to include about the surgery (I didn't think it was important, I guess I might have been wrong) was that she had to have two done about the same issue. (Not a repeat of the same issue.)
Our original vet was very old and retired a little before the surgery. A new vet took over his practice. We had him do the surgery first. The way he sewed her belly back up was horrible and had to be redone. The place she was kept before we could take her back home wasn't that great, either. When we got her back, her claws had something black caked onto them that our current vet said was probably from her clawing at the cage. She also didn't like them at all. She was a very sweet cat even to strangers before the surgery, but when she was with that new vet, she behaved horribly. And I already explained how she was afterward.
What do you mean by "the place she was kept?" Was it not at the vets' office? It should have been kept pristinely clean to aid the recovery process. Sounds like she was overly stressed which could very well lead to all of the issues you have talked about here.
Anyway, we found another vet who is also rather up in age. He redid the closing of the incision for her belly and has been very nice.
(To answer the steroids, we had tried different ways of cleaning, different dishes, different medicines, everything that was suggested. The old vet doesn't really like having to give him the steroid shots, but the acne hasn't gone away with any of what we've used, and it keeps itching, so he keeps scratching, which could get it infected. So the steroid shots were the last option for it.)
Like L4H stated - I would think food allergies is playing a major role in the acne. Change the diet to a better one and the acne may clear up. What is being spent on the shots could go a long way for the diet change.
As for me yelling at the boy cat for doing something he shouldn't.... I do yell very loudly when he gets up in the window to make him get down, because he destroys the blinds. I personally wouldn't care or wouldn't even notice him up there most of the time, but my mom hates him being up there. Granted, she doesn't yell at him. Instead, she has calmly or firmly told him to get down and/or made motions that should at least make him move. Most of the time, she will give up but still be angry when he doesn't move because of it, and the quickest way is usually a loud shout from me.
I usually get up instead to shoo him down, since someone actually approaching him (without anything that would hint at us threatening violence) is a more effective way to get him down. The reason I yell sometimes is because sometimes, I'm very busy with something and getting impatient with my mom's growing impatient commands for him to get down, or her telling me to do something about it. Because I am irritated/stressed/impatient with it, I have the bad habit of shouting for him to get down instead.
(And on me telling her to raise her voice more: She has zero sense of humor and has the worst trouble detecting sarcasm.)
Mmmm, so everyone in the house is guilty of yelling then. Not just your dad? Or at least your dad and you are? If you are training a cat you need to be consistent 100% of the time. One slip up and you are back to square one. Just yelling at the cat to get him down isn't going to do it.
L4H also asked about high cat stands. In all probability if your cats had a kitty condo placed in front of a window so they could sit and see out they would leave the windows alone. Around here it's unusual not to see cats in windows. It's a natural thing. In my estimation blinds are replaceable. Cats aren't.
How old are these people? Experience with cats, experience with vets. As in what makes these people qualified to offer advice (specifically, sugarcatmom sounds like a sales representative) how can a vet be clueless after 8 years of schooling?
It's a very good thing I wasn't drinking my coffee when I read the part about SCM sounding like a sales rep! It would have ended up on my comp screen!!! SCM has done years and years of research on feeding cats species appropriate diets. This was done after she lost one of her very own to a food recall and subsequent illness/death. 
She is highly educated and well rounded. She does not, as far as I know, get a "cut" on any of the foods she recommends.
How old are we? Most of us are fair to middlin'. 
I don't believe any of us are impressionable young'uns anymore. Most of us have had cats for years and years. SCM currently has 4 and has fostered. L4H currently has 4 and has fostered many. I have a lot.
How can a vet be clueless after 8 years of schooling? Vets do not have to take nutrition courses during their time in school. If they opt into that it is taught by reps from the very same food company that most vets push in their offices. Now if you were being taught something in school would you not believe what the teacher was teaching? Vets come out of school with a preconceived notion of what food should be fed to cats based purely on their "education" by the largest pet food company in the world. Of course they will believe. They also share a portion of that company's profit by selling their food right out of their offices. So yes, vets push dry food ergo dry food "should be" ok. Dry food isn't. It is killing cats. Period.
I apologize if any of it sounds insulting... I'm the one who came here for advice, and they're lashing out because of it.