Sorry for the scribbly-ness though.
They evolved from small, hexapodal primates that were primarily arboreal. The third pair of arms was originally for extra support on branches, and also for things like balance, tool-wielding abilities and such. They’re hairy, but developed feathers much in the way as dinosaurs did. They had long quills on their backs and arms that eventually evolved into inter-locking barbs and stuff and were capable of gliding for a few millennia before eventually developing actual flight. Now they have strong keels and wings. They still possess vestigial claws on the end of their wings, but those are hidden by “feathers”.
Aleta are similar in that they are mammalian (sort of) and developed feathers, as well as the related wyverns, but they never gained true flight. Early ancestors did glide and were arboreal, but the Aleta and the Wyverns became two separate clades over time, one developing extreme intelligence and the other flight.