Figured out what the yellow/grey one is... Spitzhauben! It's feathers are coming in and it has a little head pouf I didn't quite notice before. It's white with a bit of black in the wings. The first one died, along with all the d'uccles. They had pasty butt that I was treating but they passed anyway, even with probiotics. Still have no idea what the last one, the light brown one, is...