The dad’s brother paid for the Paris trip. He had been watching his niece (the older one that counts everyone) while he worked in Paris, and in exchange the brother paid for them to go to Paris for Christmas (and also no doubt so he could see his kids). The brother is loaded, as we also see in the second move, he is remodeling a New York brownstone in midtown.

That says, they do pretty well. It may even be the mom with money. There is evidence to suggest she is a fashion designer with all the mannequins in the house. But the following year when they pay their own way, they go to Florida and not Europe, so they are probably not as loaded as his brother.

The house costs around $2.5m in today's money, or around $1.1m in 1990. Household income would have to be north of $300k/yr in 1990 dollars or over $600k in today money.

Kevin's uncle paid for the vacation for 15 or 17 people, which would have cost over $40k in 1990. The uncle also had a penthouse in Paris(where he transferred to, creating the desire to bring the family together for xmas.), Kevin's family stayed in a suite.

Given the neighborhood and proximity to Chicago, the father likely worked in finance.

That's generational wealth. He probably doesn't have to do anything but plays at being a businessman or something. People doing mortgage calculations don't understand how the wealthy live.

The official novelisation of the movie says he is a "prominent business man" and the mom is a fashion designer.

So both probably makes quite a bit.

Certain activities pay really well.

It was the 1980s. Capitalism hadn't reached its end-stage yet.

There is a theory that he's a spy or government agent and that's also why Kevin is so good at making boobytraps

Pre internet and bitcoin so lawyer, plastic surgeon, or international jewel thief.

Whenever someone is a successful businessman, I assume either:

a) Arms Dealer, so these are all Yuri Orlov.

b) or something worse, such that if we learned about it, we'd wish it was just some guy selling used AKs in Africa, for instance the Sacklers and Purdue Pharma. Or an arms dealer who represents the United States.

His brother paid for the vacation. He paid for the trip to Florida in the sequel.

While his actual name is Peter McCallister, he had a successful line of businesses that he expanded across the Chicago area. He was actually better known as Abe Frohman, The Sausage King of Chicago.

I live right by the area this house is in. It's in Winnetka, the "North Shore" of Chicago, where all the rich execs that work in Chicago live.

And still not have enough brains to keep track of your kids

Shoe salesman probably.

Every time this comes up it needs to be pointed out that he did not pay for 9 peoples vacation, his boss did.

Mob lawyer, it's Chicago after all..

He was a lobbyist.

War crimes, probably

The NYT did a piece on this.

And what's with all the lights? The monthly fee to run so many incandescent bulbs that it looks like a nuclear explosion is occurring has got to be outrageous.

I guess one good thing with that many bulbs lit, it would save on heating.

Cocaine kingpin.

They implied that most of the extended family was only visiting, but looking at the house I'm not convinced they didn't all live in it like a commune.