First: Sand fleas are intertidal amphipods. See this link for information about amphipods. You probably already have them in your tank. The intertidal forms are obligately found in the intertidal, they will die if continously submerged, so they will not do well in reef tank.
Second: Coquina clams, are bivalves (=clams) in the genus Donax. They are clams specialized for life on wave swept beaches. Unless your reef tank is an good analogue of a wave swept beach, they will die within a couple of weeks in it. They cannot survive or feed if totally submerged. They are not the same as the clams IPSF is selling. These are a species of Tapes and are specialized for life totally submerged, and living in sand.
Finally, mole crabs, Emerita, are specialized filter feeding animals, related to hermit crabs. They also need wave swept beaches to survive, and will die without wave action. Like the coquina, they use the energy in breaking waves to help them feed.
So... all of the animals you have mentioned are interesting, but none will survive in a reef tank.