Will My Green Spotted Puffer Chew on things to Wear their Teeth down? Or do I have to feel them Hard things?

I have 2 green spotted puffers, both 1 1/2 inches.... yes, they are in brackish water and yes I know how aggressive they are supposedly, but they are fine together and yes I will watch for aggression as they get older, anyway, not what my question is. Now I know they have teeth (beak) that needs to be worn down by the puffers eating things with hard shells like snails, oysters, or muscles. Now I just came from the ocean and found a whole bunch of awesome shells on the beach, I have put them in a bleach and water solution as well as boiled them for about an hour, so they are sanitized and I placed them in the tank. I also know shells help raise the hardness as well which is good for the puffers. I found 2 awesome HUGE mussel shells, clam shells and conch shells. Will my puffers chew on the shells naturally to wear down their teeth? Because I am having a very hard time trying to get them to eat snails! I have had them for about a week and a half and I have tried over and over to try to get them to eat snails. I even tried a live crab, but I haven't been able to get them to wear their teeth down. They eat blood worms without issue though. So, will they chew on the shells, because that would be awesome if they did it themselves!