Can I just paint with Kilz and NOT wash the walls????
No. Ask the paint store (a real paint store, not Home Depot) what to wash down the walls with.
Here's what the painters did long ago, when I worked for a company that repaired fire damage. We were on-call for several insurance companies.
Tri Sodium Phosphate was the standard for this. It's similar to powdered laundry detergent. Mix with water. Wipe down the walls with a giant sponge, with another in the other hand to avoid spills on the (tarp covered!) floor. Go back over each wall with a water-rinse sponge before the wall dries.
Ask the paint store what has superseded Tri Sodium Phosphate. It may still be the standard for all I know. But don't use something you dreamed up since the paint may not be compatible with it.
Wait 24 hours to paint. First layer has to be Kilz or whatever sealer the paint store recommends to seal in smoke and tar.
I have NO advice re nuns!