No you cant sex them under 2". The bigger one is looking like a male because female yellow cons will have like a black circle patch on their dorsal fin when they mature around 2" and the bigger one isnt devoloping any black circle patches on the dorsal fin. Then smaller one is to small to tell at this point and is barely getting any yellow.
But I'm sure as with most species of Convicts they can change their sex up to 3", I've had two 2" black cons before that had no female coloring, and then one started to devolop the orange coloring on the belly after keeping just the two. So I'm sure my small one will end up female, as I would love to breed them, and sell the fry. Most LFS dont buy Convicts due to how easily they breed, but I know Yellow Cons arent readily available in the local markets so I know a few stores would be interested in buying some.