I would be somehow disappointed if the Queen wears a bigger tiara for CP's wedding than she wore to Madeleine's wedding. But maybe she has to wear the Leuchtenberg tiara because the 9-prongs will be needed for one of the King's sisters?
My guess for the bride is the Connaught tiara.
For the Crown Princess maybe the laurel tiara inherited from the very much missed Princess Lillian. But I secretly hope that she will surprise us with a tiara she hasn't worn before: the aquamarine kokoshnik.
For Princess Madeleine I think she will wear the modern fringe again.
P.S. It's still such a long wait, I wonder how often I will still change my guess
.