Your answer can be found in an old black and white 1951 movie called "Chained for Life". It starred real life Siamese twins Daisy and Violet Hilton.
Daisy was charged with killing Violet's lover. She shot him with his own gun.
The prosecution demanded the death penalty for Daisy; but if the sentence were carried out, it would mean the death of the innocent sister as well.
How did it turn out? See if you can find the movie to get the solution.