Girlfriend wants to get BF and his cousin to have sex

[TabooSappho]

I can't find any story with this scenario. The basic premise is that girlfriend is into idea of her boyfriend and his cousin commiting incest (it could also be sister or mother, but I prefer cousin). Of course, both of them are reluctant, but the girlfriend slowly seduces boyfriend to look at his cousin differently. At the same time she does the same with the cousin.

Bonus points if the cousin is really hot and kind of flirtatious, but doesn't jump too quickly in bed with them. Reluctance and seduction would be really important in this kind of story.