I've been thinking about this and wanted to post my theory about Ais:
Ais might be a Demi Spirit like the ones the Loki Familia's been fighting, except that instead of a monster, it's attached itself onto a Human. When the Loki Familia encountered the one in volume 4, no one recognized it as a Spirit except for Ais, even though Spirits are like Gods in which people can tell if they meet one. Ais has Spirit level magic and beauty, yet she's considered to be a Human, so it's similar. Since Spirits can't have children, this works as a way around it
Aside from her parents being Albert and Aria, I believe that her reaction to the Demi Spirit and her behavior when Revis mentioned Aria prove that it's more than simply having Spirit blood like Welf. As a side note, Bell mentions in volume 5 that Albert had a child, but it's never specified who he had the child with or what the child was like, and no mention of his child was included in later editions
This doesn't explain how Ais ended up with the Loki Familia but I assume the author will explain that later on. Still though, Ouranos confirms in volume 4 that the Demi Spirits in the dungeon had lived for more than a thousand years, so it might not be impossible for Ais to do the same