"Hang 'em in irons!" Nothing says medieval like a skeleton swinging in an iron cage. You can make one with foam strips painted grey and hot glued together. Just make sure to suspend both the cage AND the skeleton together so the poor guy doesn't fall out the bottom. The beauty of this is that there were no "set pattern" to the cages and every one was hand made by the local blacksmith so there is no "wrong way" to make one. https://en.wikipedia.org/wiki/Gibbeting a great visual reference, once you see it, you'll know exactly what it is.
Your idea for this dragon setup was right on! What a terrific way to use the dragons, bet nobody around your neighborhood has something like this. I always think its great when haunters show us something we just have not run across before and for sure this is it. Great Job, the people are gonna love it.
Skeleton horsemen on either or both of Home Depot's horse or pony. Opposing the dragons. They also sell bridles, saddles (if not out of stock).
As far as skeletons in cages, I have a couple. I made out of a sheet of clearance linoleum, circular sawed into strips. Painted black, looks like textured iron. Bound with PVC hoops, screws at junctures. Floor just cheap grey foam cut out of a 2x2 playroom square. Those are for trees. I could sell these things. Safe hung in trees as they weigh nothing. Unlike foam they hold their shape season after season. Nothing against foam, just harder to make look solid.
Ocean State Job Lot sold me a black iron circular tomato trellis (I guess, but it has a bell'ed top and a spike, which broke off) that spikes into the ground. Probably cost $30 bucks and looks awesome.