There are:
mortal aasimar (planetouched origins, the equivalent of tieflings, usually of human ancestry)
Aasimari Devas (immortal angelic souls in a mortal humanoid form)
and "angelic devas" - celestial angels and servants of the Gods, usually separated into three different orders.
I am not sure if current lore really differentiates Aasimari devas and angelic devas anymore, though - the difference between them is... somewhat minimal and it gets confusing when they have virtually identical names.
If you ask Aylin if she is literally the daughter of a god, she says that she was "ripped from Selune's celestial womb" - quoted roughly from memory - and considering devas can be the servants of Gods, it makes sense that the Gods may create devas themselves. Usually aasimari devas are suppose to lose their memories when they reincarnate and they don't always have the same appearance, but Aylin might be a special case as narratively it wouldn't work quite as well if she didn't even remember who she was, or if Isobel hadn't recognized her. Fun fact: Aylin is a Turkish girl's name, and it means "of the moon."
For Act 2, a lot of Ketheric's background is buried in journals and letters: