I will try my best to be brief. It seems like all I do is complain about the issue, but I feel like there could potentially be advice for me from you fine people AND perhaps a bit of perspective for others in this sub.

I worked with my MIL & SIL before I met my to-be wife. In no uncertain terms was I to ever date any of her daughters. I was a rambunctious twenty year old.
Naturally, I would up dating the youngest daughter (who is a year older than me).

The family took to me quite easily. I fit in quite well. Outside of drinking and smoking pot like everyone else, I was actually a decent guy at heart. Friendly, helpful, and relatively intelligent (I'm being quite liberal with that last one).

Fast forward a few years and I ask her dad for his blessing in marriage, which he was happy to give.
They are all insane, but who isn't?
They are quaintly racist, homophobic, and generally blanco basura.
I grew up poor, white trash, so yeah... I fit it.
However, I try to improve myself and not be racist/sexist. It's not okay to blast the n-word just because people of color aren't around.

Life hasn't always been a bowl of cherries, but I do what I can. It's become untenable as of late, though.

I hate watching baseball or football with any of them and hearing the n-word tossed about. My 28 year old niece even corrects herself when she lets slip the n-word because I chastise her about it at every turn. "Sorry, Uncle /u/NatalieJersey."

MIL was always a loose cannon. "She's a whore. Fuck that guy. He's a queer faggot. She's a coke-head." Etc, etc, etc....

What can I do? I'm not perfect and it's on them, not me... no matter how embarrassing.

Within the past year and a half or so, MIL was diagnosed with Alzheimer's. She's gotten progressively worse over time. It's not looking good.
She smokes like a chimney and swears at will. Nothing is sacred. Along with the memory problems and repeating herself worse than I do when drunk, she's become incontinent, too. We have to make sure she wears diapers all the time and even then that's not always enough. She's in her mid-to-late sixties. It's horribly depressing to see her go through this bullshit.

I came up with the idea of making business cards to hand out to random people (waitresses, servers, bank tellers, etc) saying "Sorry for anything she says or does. She has Alzheimer's. If there are any problems, please discuss it with the person handing you this card. Thank you for your support."
Something along those lines.
We don't have them yet, but I hope the family takes me seriously about it.

On top of everything else, she and her husband (FIL) fight constantly. They cannot live together any longer because they can't take care of each other. He's had health problems his entire life and continues to suffer from more than you could imagine.
They fight constantly when they're together. When they are apart, all they do is complain that the miss the other. It's insane.

They were removed from their apartment and split up among the 'kids'. MIL lives with the oldest daughter for the most part and FIL lives with the middle of five children. However, MIL has been spending two or three nights a week at the house here. FIL has been doing the same. Since winter is coming, he's supposed to move in to be closer to MIL, since my SIL lives about a mile away. In that way, FIL and MIL can be closer to each other, but not always living together.

They lived with us for a year ten or twelve years ago. It didn't end well.
My parents lived with us for five years and it was difficult at times. They have their own place now, so that's all-good.

I think if the wife and I didn't have to take care of so many other things, along with her parents, we would likely be divorced by now. Our problems are bad enough. (Trust me - I am the biggest problem. I'm no saint.) However, our mutual problem(s) bury our own issues.
I've been living at my parent's house off an on here. I moved back so we could "talk" and work some things out, but we haven't even had the time to do that. It's either here with my in-laws up our ass OR one of us is/both of us are so tired, we can't stay awake to have a conversation about anything like normal people.

I've left A TON out here, but only because this is a novel already.
I'm sorry to go on and on about shit, but sometimes you just have to vent.

In summation, I wouldn't wish Alzheimer's on my worst enemy. I may have a fuck-ton of issues with the wife, MIL, and FIL, but holy fuck is that a shit disease. It's all I can do most days to avoid scratching the back of my throat with a goddamned shotgun. I won't, but anyway....