It sounds like you're going to HAVE to move them, so just do the best you can. No matter how careful you are, moving a plant puts a lot of stress on the plant, so you probably should cut off the flower buds on the irises (as flowers take a lot of energy from the plant). The daylilies may or may not bloom - I did a wholesale moving of my daylilies last year, and I got a couple of blooms from each plant, not the usual many, so figure that that will probably happen. As for the lilac, I would think that cutting off the old flowers so they don't set seed would be enough; it would depend on how old and how big the bush is.I recommend that you check over on the Shrub forum about the lilac.
I also recommend that you get them all back into the ground as soon as possible after you dig them up, especially the lilac - have the hole ready beforehand, if at all possible.

Good luck with the move.

Joan