Here's a couple things I learned from the source code for posterity. The Kiha kill scene requires the flag "KIHA_CORRUPTION_BITCH > 0", which only happens if you had a falling out with her because of corruption (or save edit: flag =1 when left after high corrupt, =2 after corrupt drops back below threshold).
Can't find anything on Circe so I'll put what I've found here. For Circe's knowledge, there seems to be 13 potential knowledge topics (not including the manor books, bringing Jeremiah or bringing the Dullahan), 3 of which give direct spell rewards (Gargoyle, Marae, Manor), while one (Dominika) is a prereq for one of the rings. Ring rewards are given at "RewardProgress >=" 4, 6 (also Dominika prereq), and 8. However, the message that "there are no rewards available yet" is a flat response when no rewards are available, and will persist even if you've discussed all topics or gotten all rewards (also, the Dominika topic requires DOMINIKAS_SWORD_GIVEN == 1, not the sword itself).
Remaining topics:
Sand Witches (requires Magical Virility/Fertility), Crag Witches (Potent pregnancy/prostate), Kitsunes (enlightened/corrupted nine tails) Fera's Boon (Fera's Boon), Marae (Marae's Blessing), Horror (Revelation perk), Manor (Dullahan manor quest), Inquisitors (Wizard tower quest), Laurentius (wizard tower quest), Tel'Adre (been to Tel'Adre), Gargoyle (GAR_CATHEDRAL > 0), and Beautiful Sword (Beautiful Sword in inventory).