May I just add my 2 cents worth here - that this seems like a bad time to be thinking of moving a growing shrub. The weather is just about to be as hot as it gets all summer and your lilacs are putting on all the new growth that they will bloom from next year. I would at least wait until September when the sun isn't as intense and the days aren't as long.
The best possible time to move them would be after they go dormant and the leaves have fallen. If you prune them, then move them this summer, you surely won't get much in the way of bloom next year. But the big risk is that they won't survive unless you stand over them with a hose all summer.
