I definitely have the headcanon that the Boiling Isles is super OK with incest. The Blights do a ton of it, but it's sorta filtered through Odalia's control. She makes Amity kiss her on the mouth, and uses Amity to test the abomonation's sexual features, but she breaks up Edric and Emira when she catches them fucking each other because that's not her plan for them.

Clawthornes are super into incest, but since they're estranged they haven't really acted upon it in decades. Lilith has repressed her own feelings about it since the Emperor hates incest, but changes her mind in Season 2, and the whole family can fuck again like normal.

The Nocedas are on earth, and have qualms about it. Luz has been super into incest since she got an internet connection, and developed a strong mommy kink. Camila wouldn't have reciprocated her daughter's crush on her though, she's too repressed, but a summer dealing with Vee has turned her around on it. She's super guilty about what she's done with Vee in her daughter's form, but once Vee blabs and Luz is into it it's all over for her and they can start loving each other like the family they are.