OK, here's what I've learned: I'm waiting until March 1 or so to repot; I'm using well-draining soil; and I won't use a too-large pot. But I do want to divide the plant, as I have three parts currently and I'll keep the main one by itself, and put the other smaller two together. But...they definitely aren't in as good a shape, so I was going to prune those back at the time of replanting--is that OK?? Thanks for any help!!

I'm not sure about pruning all the leaves back of the smaller peace lilies because I have never done it. You can always pick them off later as new leaves grow. Find a small shallow pot that's not much bigger/wider than both root systems that are to be put in the one pot. Make sure the roots are ok and not rotting or dried out. Plants in good shape can become very stressed after re-potting, let alone plants in poor health for whatever reason.

Get as much root system for both smaller ones as you can without too much disturbance if possible.Use well draining soil like you said, water once, then not again until the top half inch to an inch dries. Don't fertilize in winter, or newly potted up plants for at least 5-6 months afterwords, and then use only half strength now and then. Put all three plants in indirect light.

Good luck!