This movie is right up my alley: Brothers of the Head
Taken from their remote family home by an impresario eager to exploit their freak value, conjoined twins become proto-punk rockers in mid-’70s England.
Other movies starring conjoined twins:
Stuck on You (2003)
Twin Falls Idaho (1999)

Have you ever read Judith Rossner’s novel “Attachments”? Very weird. A pair of BFFs decide they’re going to marry the local conjoined twins, with not always inspiring results once they do.
Never heard of it but it sounds FAB!!!!!
It’s not up to the level of Rossner’s best book, “Looking for Mr. Goodbar,” but it’s full of interesting twists and turns, and the twins come off as actually more normal than the girls do.
I’m gonna hunt down that book!