I think the mantles require holders to be mortal, not fae. The knights are always mortal. Titania and Mab were sisters and Mab drops that she was mortal in BG. Aurora was Titania's daughter, either before or after she took the mantle, so she's a question mark. Sarissa and Maever were Mab's daughters, per WOJ, by an Austrian composer in the 1800s. So, half mortal. Molly was fully human.
There's a strong argument that the leaders of the fae courts, guardians of reality, have to be mortal. I.E. have a strong connection to reality.