As long as they aren't an eyesore to you, I would rinse well with water, then dump in a pile in the corner of the tank/behind your rockwork (out of eyesight). That way your hermits can pick from the shells at their leisure. Worst case scenario, the shells act as "pod hotels". Whenever I keep hermit crabs, I always keep 2-3x as many empty shells as live hermits in various sizes to reduce snail predation (scattered in clumps behind my rockwork). I would also look for some smaller shells in addition to those larger ones.