which lived and ruled there- I'd use 'who' unless there were many royal familes and only one of them lived there
Exclamation marks- I see no need for them here. I would generally advise against using them much. Someone said that an exclamation mark is like someone laughing at their own jokes. Let the reader decide what is surprising. If you can't provide a concrete reason for using them, then cut them. In the first sentence, you might use an exclamation mark if it was the first letter for many years. It doesn't really intensify the 'thanks'.
In terms of a grade; it does the job and has very few mistakes, so it would pass. The layout/format is fine and the structure OK.
However, what mark would you give this for vocab? There's nothing in there that grabs my attention. It's sound and reads well enough, but I think you could jazz it up a bit to get into the top band. I wouldn't give this a grade A, but I think you could get there.