I would recut them into warm water with sugar in it and set them under a bright lamp that gives off heat to mimic the sun . Seems to me I have read about "Massaging" the buds to loosen the petals. Good luck!

Isn't there something with peonies where they need ants to open them?

No, they definitely don't need ants. That's an old myth, probably started because there are often ants on peonies that are just opening. There must be something sweet that they like on an opening peony, but the ants have no effect on the peony's opening.

LizaLily's information is good, thank goodness, as the wedding was yesterday! I hope Eric's peonies opened. I read somewhere to put them into lukewarm water 8" deep - maybe the depth increases the water pressure into the stems? - and be sure not to make the spot too warm or the lamp too close, to avoid browning petal edges, but those could be unimportant, nitpicky details.

Jeanne