80's Film Where Woman Breaks Curse When Carnival Comes to Town

by Rae
(Virginia, USA)

I'm searching for the title of an 80's horror movie about a woman and her best friend or sister who are at a castle/estate and a carnival comes to town, and the opening/closing scenes show the carnies dancing around outside along a path carrying torches. Along with this carnival is a mysterious beast.

The main actress is beautiful and has very dark hair, 40's style. She plays a role in breaking a curse involving the beast and this beast has an evil twin brother? In one scene, she has sex with the beast and I believe he transforms into a human or the other way around.

Does anyone remember the name of this movie?