This is the chapter that will really test your patience. A little bit of information before we start.
1. You do not get game over when the priests get near you. What happens is that when the priest is near you the crosses drains your demonic powers and when that hits 0 you get game over. This means that recklessly spamming fire balls is a no-no.
2. You can run past the priests. Yes, you can approach them just as long as you get away fast enough or before your demonic power depletes completely.
3. During Charles's level, you do get killed in 1 hit.
Okay on to the main game.
Wait for the priests to show up at the door. It doesn't matter if you only see one or two of them, just send out a small fire ball as soon as you see one.
I don't recommend you use a fully charged fire ball cause if you miss you will most definitely get a game over if they're too close.
Keep sending out small fire balls at the priests but at a controlled rate. If your demonic power is depleted then stop sending fire balls and wait for it to recover.
If the priests are too close to you by the time your power recovers don't attempt to attack them. Just run past them and go out the door they went through.
Stand on the left side of the staircase and wait for the priests to follow you, then send out one small fire ball at them. Don't send more than one in case you miss and you have to run past them.
If you didn't kill them with a single fire ball attack near the stairs, run past them and go back into the room you came from. Wait for the priest to follow you and shoot him with a fire ball when he does. Repeat this until you kill both of them.
Now the hard part comes. If you get hit by Charles's fire extinguisher it's game over. At the same time you need to keep him close to you which makes this hard. Your fire also doesn't work on him, double hard.
Lure him over to the right side of the stairs and equip your telekinesis. You need to bring that pillar down on him somehow.
Run around the pole and use telekinesis on it whenever you can. Just be sure that Charles is nearby and that in case the pillar falls it will hit him.
Try to get him to attack you near the pillar, he won't move for a little while when he attacks you and you'll be able to use telekinesis on the pillar as well as have a higher chance of bringing the pillar down on him.
The pillar has some sort of HP, but you can't see it. It doesn't actually require that you use telekinesis on it for an extended period of time. Instead you can stack up "damage" by using telekinesis on it for short amounts of time until it falls.
Another thing is you can't use telekinesis on the pillar if your demonic power isn't full. Some people use fire balls on Charles but I found it really hard to do especially since you have to wait for your demonic power to replenish after using the fire ball, so I stuck with just telekinesis and dodging.
After dropping the pillar on Charles, Lucius will walk out the main door and the credits will start to roll. That's the end of Lucius, congratulations!