They’re aquatic members of the order Cingulata (armoured new world mammals) and are related to the armadillo. That explains the mammalian characteristics and the scales.
This would also mean that the brightly colored scales are the result of light scattering structures in the scales as opposed to pigment as no terrestrial vertebrates are capable of producing pigments other than brown melanin and yellow-y orange-y carotene. Birds have structures in their feathers that refract light to create the appearance of color without pigment (also this is how blue eyed and green eyed people get their eye color)
also they’re probably sort of like seals (spending a good portion of their hanging out and socializing and stuff time on land because they seem to lack a blowhole and the like and have necks and hair and other features that mean they’re not totally adapted to living completely under water but hunting for food in the water). Also they’re probably tropical because they don’t have enough of a blubber layer to prevent too much heat loss for colder water
and the scales make sense if they actually spend a fair bit of time dragging themselves overland (so they don’t scrape themselves up/irritate their skin). Also based on their jaws they probably cook their food
Thoughts From The Peacock Angel 