"Birthday Surprise" has an asinine premise, merely used to get some mechanical threesome action underway. River Fox is certainly sexy playing an unbelievable character, who's coming of age at 18 has long been looked forward to her fake parents, who stole her from the hospital as a baby in hopes of having their way with her sexually when she's "legal". Instead of getting mad at Sarah Vandella and Tommy Gunn she embraces the concept and a hot threesome results.
This bit of idioicy certainly fits in with our current political era, where lying, cheating, projecting has become de rigeur for Trumpian Republicans to hold onto power.
For pornographers, the incest gimmick is inventively exploited by having the girl unrelated to her putative parents via the kidnapping, yet the entire episode makes light of the real-life phenomenon (and prevalence) of incest where young children are abused by real parents or other relatives who have power and proximity to take advantage of them. To say this is in poor taste is a vast understatement.