Based on the body shape, I'd guess they're a type of stone crab. These ones I'd segregate or donate, under the assumption that they'll be impossible to track down if they turn predatory and live in the rocks ... the other crab you posted, the hermit, has a mini refugium growing on his back. I'd be inclined to leave him in, because if he was predatory he probably would've scraped the barnacles and dusters off his shell and eaten them. He'll also be easier to locate and observe than the other type, so you can monitor him and easily remove him if need be.