As for Caesar Island, it's a good idea to have a special item that lets you move again. If you don't have any of that, then hopefully you've saved somewhere where you can buy some. Also, use characters that move really far (for some reason it seems movement is governed by the weapon you have equipped) and you'll probably need to use a character that can fly over those gaps.
As for blood-sucking demons, they keep coming back to life so you have to time it so all the enemies are dead at the same time. It's probably a good idea to try and keep them stunned for most of the battle.
