Are they THAT heat sensitive? I'd hate to lose them all. When, and how severely, should I prune? Take the more damaged ones back down to sticks and hope for recovery?
A. That is what a full-sized Pittosporum is supposed to look like. I like the color in the form of the undamaged plant.
The damage top and suckering from the base tells me the plant is putting on some new growth where it is easiest for it. When everything is optimum, the plant will always try to get larger and put new growth as high as it can. When conditions are not optimum, then it will try to put on growth in places where it spends the least amount of energy and trouble.
The damage at the top in the suckering at the base tell me the plant is not getting enough water when it is watered. Plus it was opened up with some pruning cuts at the base. I would add 2 or 3 more drip emitters to the base of that plant and try to cover at least half of the ground under its canopy with water. This means spread the drip emitters out about 12 to 18 inches apart under its spread.
I would also put about one bag of compost under the large plants and water it in with the hose. Keep the area wet for the following 1 to 2 weeks. I think you will see a change in 2 to 3 weeks. Prune out the dead branches by cutting at a Y or joint between the dead branch and a living branch deep inside the canopy, 8 to 10 inches inside of it.