Most Cordylines like to be slightly crowded. I wouldn't expand more than about 3" per move, and only if they are pushing themselves up in the pot. Be sure to use a fast-draining mix suitable for alpines or succulents, or mix sharp sand and pumice with a standard potting compost. If a lot of the soil falls off of the roots, remove about 1/4 of the leaves, starting with the oldest.

Good Luck!