Here is another photo

We can't help ID the plant unless you show us a close up of some foliage on a better shrub. The 'skeleton' of the sickly specimen looks like no Pittosporum I know of. Perhaps a Ligustrum (privet)?

Were all of these poor shrubs recently sheared?

If healthy, pittosporum or privet (and many other species) will regrow beautifully if cut cleanly all the way to the ground in what is called rejuvenation pruning. It is best done just before the spring growth commences. I don't know when that might be for you.

We'll know more when we see further pictures.

This one is second in line with plants in between. They are lightly trimmed occasionally.

Col047, did you miss Rhizo's response?

It looks like rather severely clipped Pittosporum tenuifolium to me. Am I right in thinking the problem is starting at the base facing the lawn each time? Do you have lawn sprinklers? Could they be keeping the foliage moist and attractive to funghi?

Or do you have verticillium wilt in Tasmania?That can cause areas of shrubs to die off.

Colo47,
The one that is almost all brown, is pretty much dead,
I do not know where you live.
Are you in the US?
Anyway, just DO NOTHING to them.
Pittosporum are extremely hardy shrubs, especailly established ones, you have older shrubs.
Have you moved into this house recently?
What has changed? Did they look nice? When?
No fertilzing them, just make sure you water them good by hand when you haven't had rain for about 10 days.
By the way, the rocks are frying them if you live in a warm climate zone. They hate rocks by their roots.
They love mulch.

Thanks butterfly4u. As I said in the original post we live in Tasmania Australia. It is a cold climate so no problems with the pebbles. We have removed the tree.