pseudoincest

noun2

1. •
   Sexual involvement between family members who are not blood relations (e.g., siblings by adoption, stepparents and stepchildren, in-laws).

   • Half of the cases were the classical father-daughter incest, a quarter of them the stepfather-stepdaughter pseudoincest and the remainder were abuse by relatives or siblings. — 1986
2. •
   Pornography or erotica focused on sexual situations between nonconsanguineous relatives.

   • (Moore explains, for instance, that in 2015, pseudoincest porn was a popular genre.) — 2016