These all look really great Shadow!
For the female Duros, I confess I'm not familiar with the species, but if you want to make her more feminine you could try slanting the eyes a little, making the chin a little more slender, and thinning the neck. In illustrations, men's necks are usually as wide as their heads, but women are more often portrayed with thin necks, like their heads are ping-pong balls on pencils. (Well maybe not that much but you get the idea. XD)