A few Hermodice? These worms are extremely rare in the hobby because they're only found in the Caribbean. If you've got more than one you should play the lotto because you've beat some really high odds. A foot-long Hermodice would be much wider than your pinky too.
This species does not eat healthy fish either. They couldn't if they want to because they have no jaws or any other weapon to subdue their prey with. The spines are purely defensive and extremely fragile (and not venomous). These guys are predators of sessile inverts like corals. The literally lick their prey to bits. Most fish won't sit around and wait for that to happen.
It sounds to me like you've just got several large specimens of the common, harmless fireworms (Eurythoe). If you do have Hermodice it will be active almost exclusively during the day and will come out in the open without fear of predation. You will be able to see a big red tuft on their heads when they're out. Eurythoe has one too, but it's much less prominent. If you have any doubt as to whether your worms have the prominent tuft, they don't.
If you have Eurythoe and don't feed the tank, you could starve them out, but it would take a long time. Your best bet is to leave them since they're harmless at any size. If you feel that you have to get rid of them, you can trap them using a piece of pantyhose with some seafood inside. Their spines get tangles in the fabric. If you have Hermodice you would have to remove any corals, tube worms, sponges, and other sessile inverts to starve it out. Again, it would take a while to starve. Your best bet in that case is simply to find it out in the open and remove it with tongs. This is fairly easy to do since this species is active during the day and not skittish at all.
