I can't get out of the boss fight. As soon as I exit through the menu and want to use "Continue" (or press "Retry" after death), I am brought back to the battle.
(I shouldn't have gone weak against the twins without making a save)
Yeah you can't really exit it. You will have to go back to an older save. The continue will be the same thing as the game autosaves before entering a bossfight. You will have to either defeat them or rollback, sorry