I never EVER interfere with the seed casing... that's just asking for trouble when you don't need it. The plant will get rid of it naturally as it grows and will, honestly, probably be stronger for having to fight that battle!
Good luck!
Sometimes you have to give them some help. Looking at the top left pot i would mist it and help take it off. Just have to be careful when you do it. On a seedling that has a piece of shell still on you can also mist to help it fall off naturally or remove if you want.