How old are your lilacs? I have several 40 year old lilac bushes that are not blooming well any more. I’ve been told that I should prune them half off and wait 2 years. They should come back strong the 2nd year.
But, I’ve also noticed that nobody’s lilacs are doing well in Wisconsin. I think it might be our strange weather this year.
Do not trim your lilacs!!! They hate that!!! It cuts off new growth, and they will not bloom for a long time!
Old time gardeners fed their lilacs vinegar water because they like acid soil.
I’d consider using an iron/sulpher solution.
I think keeping the yard too tidy can be a problem. I think they like dead leaves left over the roots.
I learned the hard way about trimming.
Just my thoughts.