Seems like a similar story with most indies... we also started off doing this as a side project just for fun, 2.5 years ago with NYZ 1. I was a teacher, another brother worked at NY Times, and the 2 others were doing freelance. When NYZ 1 did much better than we expected (we weren't expecting much), the prospect of actually doing this "for real" became apparent. At that point some of us went full time, some of still part time for our 2nd project Bug Heroes (we charged up our savings to supplement NYZ 1's earnings)... when BH also did well (actually it didn't do that great until we went free + content pack add-ons), everyone went at it full time.
With the way the App Store is changing though (and because of some experimentation), we definitely over-achieved with our first 2 games (though NYZ 2 has done well so far, thankfully), making the last year pretty tough. We've had our ups and downs (some months barely being able to scrape by, pulling money from savings), but we also haven't tapped into any local resources like business loans or signing on with publishers either, so there are options. Really we're just working game to game, praying each one makes enough to sustain us until the next
At the end of the day nothing quite beats working your own schedule, doing something you absolutely love to do