It's been a while since I stopped playing half way. But these courtesan characters, do they ever stop being "active"? If not, I think I'll just stick to Kaywin in subsequent playthroughs lol
Practically speaking none of the girls are "active" after the introduction. To begin with, everyone besides Kore and Thassia has little interest in "laying down on their back for money" while Kore and Thas do it for "lore" reasons but to my knowledge (unless you choose to do so) they never bang anyone besides the MC.
Even still you have the option to start 1 out of 3 types of relationships with the girls:
1.Monogamous - Both the MC and the girl are in a closed relationship so they can't sleep with anyone else (if you do the girl breaks up with you)
2.Open Relationship - Both the MC and the girl are in a relationship but can still sleep around
3.Harem - The MC is in a relationship with the girls in the Harem but they can't bang anyone else
(Yes I know they're self explanatory but alas)
I don't remember if the relationships are hard-coded or it depends on trust but from what I remember everyone accepts a mono relationship, Diana and Zafra don't go for open/harem and Isu and Windress refuse the Harem path.
Take this information with a grain of salt tho since I didn't play in a while and I just started a new run so I didn't really delve into the whole relationship aspect.