I think the Epsom Salts would be fine, and if it were me, I'd be more concerned with the Tylenol #3's.
If I were you I'd try a mild liver cleanse, as you don't want to upset your babies, and make them come early! Twins sometimes come earlier than 40 weeks.
Just taking a tbsp of olive oil can ward off a gall-bladder attack, feel free to take two tbsp.