Well they are not whiptails for one thing. They are Farlowella or "twig" cats. Probably Farlowella vittata as that is the most common species imported although there are several species that are very similar. Males will have longer bristles on their nose called odontodes. Females will have fuller bellies when ripe with eggs. You can find more information at www.planetcatfish.com.
the one on the log looks like a male they have wider snout with , females have thinner snouts ^_^ males also have tiny bristle like things on there snout you can feel them with your finger, males are more slender females are more rounded in the tummy area.
I recently got a 6inch( believed to be) female ^_^ looking for a male!