looks like a brittle star...safe for the tank.
I'd skip the crab unless you can 100% identify it as safe for fish and corals. many cute little crabs grow up into fish eating monsters. uncool (I just had to remove a crab from my tank that I decided was 'probably ok' when I first set it up).
As far as the shrimp goes, hard to say. Could be a cleaner...could be a mantis or pistol shrimp. If it was me, I wouldn't add them without knowing 100% what species they are.
Former advisor and planted tank geek...life's moved on though.