My Fiancé's Parents Own A Puppy Mill. How Can I Report Them While Covering My Own Butt?

Long post incoming. Thanks to anyone for reading.

I (20f) and my fiancé (23m) live with his parents in a large home out in the country along with his 2 sisters, his brother, and his sister in law. We live here out of convenience due to some medical problems he has been having affecting his ability to work, so funding has been tight. Recently, we had a bit of a breakthrough and found a med that will help him tremendously, so he is searching for work again, at which point we will double down on moving out. We have 4 dogs, which makes renting hard, so we are going straight into buying our first home.

I have been living here for 2 years as of this July and to say things have gotten worse is an understatement. They have easily over 100 dogs (probably close tob150), majority of which are unfixed. They spend most of their time in a room full of kennels lined up against the wall except for a select few of their favorites who they give closer attention. Some of the dogs roam freely in the downstairs portion of the house, and none of these dogs are potty trained or have an ounce of any training for that matter. Shoes are a must in the house to avoid stepping in pee or poop.

They have one dog who has been bred every single heat since her first, and have had so many accidental litters I've lost count. Most of the time they can't even sell the dogs so the population just grows and grows. The dogs are left unsupervised if they are not in a kennel, which means they destroy stuff, inbreed, and have broken out of the fencing on many occasions.

One of their dogs has charged and attacked my 1 year old lab several times for simply walking past. Their dogs have bitten all of us in the house at some point. They are fed the incorrect amount of food, they only get out for like 3 hours a day, it is miserable.

They also have around 10 cats. They rarely clean the litter boxes, meaning there are hundreds of flies around them at any given moment. One of their cats has severe allergies they know of but won't treat due to money, so he is riddled with bloody scabs and congested all the time.

My question is how I can collect evidence and get them reported while covering my own ass as much as possible. Once we are completely out of the home with all ties cut I want to go all out on getting them reported so these animals have a better quality of life. I feel horrible having been a bystander all this time because I fear my dogs (and myself) will get caught in the crossfire so I can't do anything.

Who would I report this too? What kind of evidence would I need? A lady they had problems with once before had tried to report them, but because they were "fed and clean" there was nothing to be done. So I want to make sure I do it right.

They were also quite cruel and vindictive to that woman, and so I want to ensure they can't trace it back to me as the reporter so they can't take "revenge". Any advice would be so appreciated!

ETA: I am in Wisconsin. They have a kennel license but I'm not sure the specifics on that so I'd have to look into it more.