Disneyland to DisneyWorld is 2506 miles. Assuming an average of 65 miles an hour (yes, there are places you can hit 70-75 and still not be pulled over, but getting out of Anaheim you'll be lucky to go 50, lol...so it's an average)...so it's about 38 hours of driving.
Figure out how many hours a day you want to drive and plot your course. My route would be something like:
It's about a 6 hour drive from Disneyland to Phoenix, which would be a major city to stop in....or since you'll then turn south to continue on, you could add another 1 1/2 hours or so and be in Tucson. From there I'd plan to get to Las Cruces or El Paso on day 2. The drive across Texas is a long one....it's about 600 miles or a solid 8 hours of driving to get from El Paso to San Antonio. No major towns really in between, but lots of Texas BBQ to eat and tumbleweeds to count. If you want to push harder Houston is another 2 hours or so past San Antonio. Next head for either Baton Rouge or forge on another hour to New Orleans. That leaves about 600 miles, 9 hours, to get to Orlando.
I've driven from Phoenix to Orlando and back.....with kids so I was the sole driver. I can tell you that 8 hours behind the wheel is nothing....until the second or third day of that long schedule. We had music and audio books to listen to, took a lot of stops to see whatever suited our fancy along the way (which added to the length of the day since we did the stops I suggested above so some days were 10-12 hours between hotel beds to collapse on).
If both of you will be driving it will be much easier because you can take turns....personally I'd suggest 2-3 hour shifts just so you have an excuse to stop and stetch your legs for a minute and so you don't really feel like it's never going to end, lol.
If you've got the time (and we did this a second trip and enjoyed it MUCH more), then I'd plan about half that many miles each day and stop and really enjoy the sites. Our second trip I had the girls do some research about what we could stop and see in the way of sites so we have it planned out better. Was nice to also be able to plan ahead and book hotels to get cheaper than walk in rates....but now with smartphones I wonder if you could book it a few hours away and get internet rates?
Have a fun trip!