I don't think that first one is a chiton. Looks more like some type of nudi, or maybe even a baby sea hare. Hard to tell. Chitons on the other hand are the things you see in tide pools stuck to rocks. They look like a prehistoric pill bug, flattened out and cemented onto the rock surface. They have very distinct hard sections of their back, giving them the pill bug appearance. Very small varieties are sometimes found in reef tanks and they are harmless grazers, as far as I know.
More likely than not it probably will starve to death. Most nudi's have very specific diets that cannot be successfully matched in a hobbysts tank. If you get a better picture look up the sea slug form (I do not know the address), they are great for identification.
The first one is a tritonid nudibranch. Most species are specialists on soft corals. Second is a cerianthid anemone. These build tubes in sand & mud. The third... What are you asking about? The harlequin shrimp? They only eat sea stars.