With some obvious exceptions, identification of invertebrates from photographs alone is generally difficult. The accuracy of the identification will vary between taxonomic groups but with sea stars most you will only be able to identify to family or genus at very best. The sea stars here are almost certainly in the family Asterinidae and could very well be Asterina, but as to the species, that could only be determined by microscopical investigation. Without knowing the species and the feeding behaviour of all possible species, it is difficult to be definitive about what they will or won't eat.
I have seen photographs of sea stars that "look" like these feeding on corals. Are they the same species? It is not possible to tell. Will these ones eat corals? It is not possible to tell.
At this point, I believe all you can say positively is that they are sea stars and they are opportunistic. As with any hitchhiker I find in my tanks, I say give them the benefit of the doubt (innocent until proven guilty), but watch them closely and be prepared to act quickly.