It is possible it did at some time in the past although I have serious doubts and did a whole run down on what I thought it was bringing in currently (not nearly enough to support their outgo right now and way short of 30K a month, more like $3K a month right now). I think they probably did make more, possibly significantly more, although I doubt 30K a month at some point in the past, but that assumes a high volume of sales through the two smallest Mormon oriented bookstore chains, Deseret Book and Seagull Book. Not of their books appear to be listed on the website of either of those now.
This is a lot of my opinion, but opinion based on some knowledge beyond the average of the economics of the publishing business. (Most authors dont' actually make that much, a very small percent enough to support themselves without another income source.) Here's a question to ponder. If Chad was bringing in 30K a month in income, why was Tammy working a relatively low paying job as a school librarian? It could be because she loved it, but I'm betting it is because they needed the money.