It shouldn't eat the clowns. There's a risk of it happening, but most clownfish are smart enough to slowly get acclimated to the anemone. An adult bonded pair is going to know to be careful, and the risk of being eaten is low. I can't say the same for your other fish. If they bump into it, it's game over. They'll probably avoid it when they can, but if they bump into it while asleep or after being startled, it'll get them. The yellow tang is going to be at the highest risk of your fish, they love to dash about without seeing where they're going. That being said, it won't go on a rampage and kill everything. Plenty of people have these, and don't have fish eaten very often. It might be a good idea to try and get it to stay out in the open on one end of the tank, that way the fish'll be able to keep away better. It could go in a nano tank, but as well as the clownfish, it'd be the only living thing. They can easily get to be 12" wide, and 18" isn't unheard of. I wouldn't try to keep them with other fish in a tank less than 4'. Good luck, they're very nice anemones otherwise.
