Lilac tree disease

greenstead

We have three Lilac trees. They have been great for years. This year all three seem sick.
The top branches are bare and look dead.

Help please.

Dovefromabove

That looks as if its starving ... the rhododendron (if that's what it is to its left) doesn't look any better.  They might've been parched too ... growing in the rain shadow of a high wall ... how much soil are they in ... are they fed and mulched etc? 

Borderline

I agree with Dovefromabove, the other plants there don't look too well either. Looks like the shrubs are suffering from lack of water and feeding, possible over shadowing going on too. Is that a Sorbus tree to the left? The area looks very crowded and it would be interesting to see what the soil looks like. The roots from the tree will be competing with your Lilac shrub.