There is always a chance, but the number of jack stands isn't going to stop it if it shifts. Also just be careful while doing it I work under vehicles all the time on jack stands (school buses), but before that I worked at a Ford dealer. I think working on them on a lift is a little safer because you are on your feet, and it is easier to move. However you got to do what you got to do.BTW if it helps you can place ramps under the wheels incase it does shift they may help slow it down.
Creepy stuff right there. I've seen guys under a car with just a jack holding it up and that freaked me out. But I guess you're taking a chance just walking out the door in the morning.