They don't...
No.
Simply stated, No.
It is illegal for an immigrant with a visa to stay in the U.S. more than what they are supposed to. It is not illegal to have kids or to work here, but it is illegal to hire that person.
As far as I understand it, anyone who is not a Canadian citizen/immigrant/permanent resident, you need a work permit.
=An immigrant is NOT an alien.==The immigrant would still be legal because they were married to a US citizen.=
Yes, you can work at McDonalds if you are not an illegal immigrant.
The person working will have a work permit or landed immigrant papers this is up tho his employer to see it, otherwise it really is no one's business, which brings into question, how does one really know whether the person is illegal or not?/
An illegal immigrant is someone who, without permission, enters a country to live and work.
Yes this is very common
Yes that is the best way to do it?
No
Yes, but you would still lack the legal right to work