I'd probably establish one before the other. Put the multi's in a corner of an empty tank. Let them get established, then add the rock pile and caudo's. When the caudo's start to get some size, add a few shells near their rocks. Let the multi's get established a bit by raising some fry, so you'll know they'll push the caudo's out if they get interested in their turf. I don't see caudo's going after and killing multi's like some lamps are known to do. They could still compete no matter what you do, but I like some interaction between two species as long as it's manageable. You've got a lot of room in a 30B. The worst aggression with caudo's in with their own kind, but I have a group that lives in close proximity, 2 pair and a single male, and they seem to have an understanding. Even if/when multi's migrate to the rocks, I find that the caudo's orient themselves to rocks, but really don't spend much time, if any, in the rocks.
HTH