I have a sandsifting starfish and a pink/orange starfish will they eat my electric scallop?

The Sand Sifting Starfish won't cause any problems, and if the other star is either a Fromia or a Linckia, it will be fine with the scallop as well. Just note that all of these species need a mature tank, and the scallop should be offered a food designed for filter-feeders several times per week.