In advance, using royal icing, make 350 tip 129 drop flowers and 400 tip 225 drop flowers, all with tip 3 dot centers. Make extras to allow for breakage and let dry.
In advance, cut path pattern from triple-thick cake board. Wrap board with foil and ice smooth with royal icing. Edge with tip 4 beads, attach flower clusters and add tip 352 leaves in royal icing. Attach flowers to edge of horse and carriage ornament with icing.
Ice 1-layer (3 in. high) cakes smooth in buttercream and prepare for
stacked construction. Using Cake Dividing Set, divide 10 and 12 in. cakes into 12ths. Pipe tip 3 double drop strings, the longest 1 1/4 in. deep, between division marks. On 8 in. cake, pipe tip 32
crown border, spacing shells 1 1/2 in. apart. Pipe tip 3 double drop strings 1 3/4 in. deep, between shell bottoms. Attach tip 225 drop flowers with dots of royal icing to each shell and at points of all drop strings. On all cakes, pipe a tip 32 line of icing at bottom border; attach flowers in both sizes; add tip 352 leaves in royal icing.
At reception: Position a dowel rod, cut to fit, in bottom cake where castle path will rest. Position castle, horse and carriage and path on cake.