clove polyps. One of the blights of the marine aquarium. IMHO, your best (easiest) method of getting rid of them will be to remove the rocks from the tank and let them sit outside in the sun for a week or so. Then scrub well to remove the dead material and reuse.
The Green frag in the 2nd picture looks like some sort of palythoa. They, too, can spread like crazy and can also potentially harm you on contact. Use caution with them. Consider isolating them on their own little island so that if (when) they begin to spread you can more easily control them.