Lovely Pics!!!! They all look like brigs to me. The purple one may heal if he is getting enough calcium through collard greens. How big are they? They look small.
I just had my cana lay eggs on the top of my filter hood! I don't know for sure if my one other snail is a cana or not yet. The egg mass (clutch) was bigger than a leech! I know for sure that ol' Blue is a brigs, and therefore cannot mate if the other is a cana.
Here is a pic of Buck, the one I am not sure on:

It is rather an old photo, but I was told he may actually be a dark cana. If he is?!! Wow!
Do you have other fish in with them? Their anttenae look way too short.