Im in a relationship where my wife's parents are bums. My wife's mom is still living off her 82 year old mom and she won't get a job . My wife's dad has no job either. So the day before our wedding her dad took a train into town, we had to pick him up and he did not rent a car. So he borrowed my fiancées car and now she can't get around town to do the things she needs to do to get ready. Plus he did not rent a hotel he is barging in on his 89 year old mom and staying with her. And he brought a bum friend with him from out of town. Then we pick her brother up from the airport and he is drunk as hell then we take him to the store after and he throws a fit out of the blue takes his shirt off rolls around on the ground and storms off yelling in a drunkin rage. Then her mom isn't planning on renting a hotel she wants to camp in her truck outside of our house. I just don't know what to do. I end up fighting with my wife a lot and I don't like to fight or argue.

Ask your wife what she wants you to do regarding your family, if anything. Whatever she asks of you, do that, and do it happily.

Family is a unique situation. Unlike friends and dating acquaintances, extended family is a "take what you get" prospect. You can't change them, you can't truly avoid them (at least not during the wedding process), and you can't strangle them. *sigh*.

So, sometimes you have to "go along" to "get along". Don't overthink the extended family's issues. DON'T. Their problems are THEIR problems. You will politely work around them when they try to interfere.

Priority:
Always protect your wife/fiance first and foremost.
Even if inconvenient, help them where you can, especially if it includes situations where not helping could adversely affect your wife/fiance.
When in doubt, ask your wife/fiance and follow her instructions regarding her family.
You don't do these things because it is right to, you don't do it because you're trying to actually SOLVE anything, you do it because you love your wife and that is all the reason you need in an enduring love.

Love is not bothered by inconvenience.

So is this person now your wife or still a fiancée?

The mother wanting to camp in her truck outside your home is not mooching off you.

The father staying with his 89 year old mom is not mooching off you either.

You didn't discuss what brother was doing for accommodations either. From his behavior I would definitely say he is bipolar with the ripping off the shirt and yelling and screaming on the floor when drink. Have seen this particular performance a few times from bipolars so I know this is a favorite performance of them.

Your fiancée did give her father her car to use.
She could have said no. He was supposed to be staying with his mom.

I think your main concern here is just WHEN are they going to literally move into YOUR home and mooch off you. I feel your dread at this happening very soon.

If you don't like HER relatives then I suggest you call off everything and go your own way as the old saying goes "You can pick your friends but you can't pick your relatives." holds true in this instance.

I still don't understand your use of the word "mooch" either having read your post several times now. Just where does this come into play here? You are annoyed that her parents live with their parents and have no jobs? Please explain.