Her dad has always sounded like the curmudgeon type to me, which I don't really mean as an insult. I always doubt her version of events because she views everything (everything) through such a distorted lens, and she'll skew anything to fit her victim narrative.
If she says her dad has OCD, I tend to assume she's pathologizing a personality trait: maybe he's just tidy, maybe he's a full-on neatnik, but she has to knock it up a notch and assign an actual pathology to it. It's the same way she can't just like plants: no, she has to be africanvioletgender (I cannot remember her actual word for plantgender).
Not everyone gets along with curmudgeon personalities, and it's probably a bad match for someone whose core personality trait is sped. He's also under an unreal amount of stress, and that kind of constant, unrelenting worry doesn't bring out the very best in many of us. His wife's cancer is in no way her fault, and I imagine it must feel like Staph is being deliberately difficult and adding more to his load.
My heart does break for them, because their adult daughter should be the one fussing over her parents, telling her dad to take a break, bringing meals over, taking time off work to drive mom to some of her appointments. Instead, she's getting scammed on a monthly basis, requiring frequent finical bailouts, camping out at their house, and now trying to add yet another responsibility-- a cat she can't care for-- to the mix. Her apartment is probably as dirty and smelly as she is, but I also wouldn't be surprised if only a minor mess did cause her dad to explode, given everything else (gesturing at the past 1300+ pages).