Jim Bob and his parents were in real estate, which has generated income from rentals and buying foreclosures and then selling for a profit. JB also has a cell tower on a piece of his property, which generates a nice chunk from what I've read elsewhere. Since the show, they have income from TV, books, and People magazine.
Josh "owned" a used car lot before moved to DC. I think JB really owned it all along but on the show it was made to appear Josh did.
John David has a towing business and a pilot's license.
Jana, Jill, Jessa and Jinger are simply uteruses waiting to be filled, so they have no jobs. Jana actually mothers the majority of the children since Michelle seems to think her obligation ends when the baby isn't breastfeeding any more.
Jill's husband Derek worked for Wal-Mart - he actually has a college degree - but quit a few months ago to pursue being a missionary (i. e. soliciting donations and flying back and forth to a foreign country several times).
Jessa's husband Ben "works" for Jim Bob, doing ??? No one knows for sure.
Joseph and Josiah are both over 18 but I don't know if they work. Josiah was shipped off to the ALERT! academy for a year or two...I strongly suspect he has homosexual tendencies and that's the Quiverful way of de-programming the gay. Shortly thereafter he was announced to be in a courtship with what seemed to be a reasonably intelligent 17 year old - who proved her intelligence by ending the courtship after the molestation was revealed.
I really need to get a life...I know way too much about this family.