Hey! Sorry if this reply is really late, I’ve had no access to a computer for a few weeks and the app is pretty “meh” when it comes to notifications.
If you’re looking for castles then Edinburgh Castle would be the obvious one. However, there are loads of castles you can visit. There’s Urquhart Castle on the banks of Loch Ness, Stirling Castle, among others, some ruins, some not. There’s a whole Wikipedia page with a list of castle in Scotland, which would be a great resource. It is called “List of Castles In Scotland”. I’d add the link but I’m on my phone unfortunately. Sorry! :(
As for dressing up I’m positive there are more than a few places out there where you can do it, not just at castles. You’ll have to look the castle/attraction website up or phone to see if they do dressing up, unless it is stated on their website. A lot of the major, popular castles have websites telling you about different events they are running.
I hope this helped!