beigledog- as long as those lilacs are under the shade of a tree they will always bend and stretch to find the sun. Have the same thing myself under some pine trees. Remove the one not producing as it may have a virus that could spread to the other. One thought- oak trees like pines have acidic residue(leaves, etc) and lilacs like their ph on the higher (alkaline) side of the scale. Don't try digging out the roots. Much easier to nip anything that might spring up in the next couple of years.
..........al
I may not agree with what you say, but have fought and will continue to fight for your right to say it. USArmy 1966-1975