The one in the center appears to be a branching variety and those are pretty easy to frag. Just use a band saw or dremel and cut the skeleton under the polyp head. You've got the polyp itself and then usually an inch or two of "flesh" that runs down the skeleton and then it's just bare calcium skeleton. Sometimes you can even use a pair of hand cutters to cut the skeletal stalk but that's a little more risky because it can break and crack and there's not a lot to do in order to control where it breaks. Heck, you might be able to break some of it with your hands.
I don't have any experience with the "wall" variety of euphyllia but the branching ones are pretty straight forward.