Those are all shrubs, unless you plant a Korean lilac grafted onto a trunk or trained up to have one. Then you have a small, sort of faux tree. Some spiraea produce fairly large fountains of growth, maybe you are thinking of a dwarf kind of Japanese spirea. Ninebark definitely grows large, unless you choose a dwarf/compact selection.

For color harmony maybe avoid a Japanese spirea with yellow foliage. Although one with light yellow leaves might brighten the grouping without producing a clash. Otherwise, I'm thinking you would have a mostly pink or pinkish flower theme (based on the lilac) with complimentary purple foliage from one of the purple-leaved ninebark cultivars ('Monlo', marketed using the selling name Diabolo) probably still has the best leaf color).

Maybe put a 'Monlo' or two behind the (tree shaped) lilac, with several dwarf Japanese spiraea underneath the lilac.