Hi Afstocker, lilac,s will grow in any fertile soil, in full sun or part shade once established, they resent being moved and may sulk for a while afterwards, I think you may well get flowers next year, once they,re established they need very little attention, and usually flower every year.
Welcome to G O Y , Derek

Get some "garden compost", "planting mix", or "forest mulch" from the local nursery, and put it about an inch or two thick, from 6 inches away from the trunk out to the the outermost branches, and scratch it into the surface, if you can. Doing that every spring and late summer will gradually improve the soil, and much more cheaply than by using potting soil. Composted manure would be even better, if you can stand the smell. Meanwhile, don't prune the bushes from late summer through their normal blooming period, since that will cut off the buds before they bloom. And be patient--older kinds of lilac can take 5-7 years after planting to bloom.

Thank you so much for the suggestions. I've never tried to grow lilacs before. I'm going to try the "garden compost" to improve the soil and I'll try to be patient. Thanks for the heads up about moving them since I had considered that too.