Mikeangel, My hubby and I started expediting in Oct of 2007 because we were both out of work at the same time and desperately needed an income. The first few months were a huge adjustment period and only the real need for the paycheck (we drive for a fleet owner) kept us out here.
Below is just items that your mom and step-dad need to think about and discuss, and is not at all meant to be a discouragement, rather a reality.
Learning to cohabit with your spouse 24/7 for weeks at a time in a tiny little "box" takes a lot of willpower and "grin and bear it". Learning to sleep in a moving, bouncing, noisy sleeper takes patience and persistence. (I'm STILL trying to master that.) Learning to drive a truck (even a straight truck) in winter weather can be nerve-wracking. Even driving a truck on a beautiful, sunny day in rush hour clogged traffic through a big city can wear on the best of drivers.
Showers do not come every day, and a lot of times truck stop showers leave a lot to be desired. Part of the process is learning where to stay and which places to avoid and usually is just a matter of trial and error. As others have stated, load amounts vary from week to week. Some weeks they may run every day, while others they may find themselves sitting more days than they run and they will need to be able to adapt to that.
To be fair, no one told us this was going to be an "easy" job, though no one told us how trying and difficult the first year was going to be either. It takes a boat-load of patience and perseverance, will-power to succeed and willingness to do what it takes to make sure you succeed. We are still out here because we have come to love what we do. Both the good and the bad and we take it all in stride. It is a "lifestyle" that you really have to want to adapt to or it won't work.
Your mom and step-dad really need to talk about everything that goes with the way of life on the road and make sure they can both adapt completely. It's more involved than just the weekly paycheck.