I'm going to start with nutrition. Unfortunately, adult brine shrimp does not have much in the way of nutrition and can't sustain a fish long-term. Freshly hatched baby brine is better, but is only so for the first day or so, after which it loses that. Mysis shrimp is a much better staple, and nearly all my fish including my clowns love the New Life Spectrum Small Fish pellet food, which is packed with good stuff. Another thing you might try for a while if they're having trouble accepting that stuff (mine couldn't eat the mysis or pellets until they grew a bit) is Nutramar Ova frozen prawn eggs, or frozen cyclop-eeze.
I notice that his gills are looking inflamed. Ich in the gills or gill flukes are suspect.
The other fish does not appear inflamed but does look really thin. They may both have internal parasites. I'd put the surviving clown in QT and treat him with PraziPro. That should remove any flukes and/or internal parasites. Change the diet without delay. If he doesn't start acting more normal or at least eating within a few days, I would repost with a current photo.