Is this a good idea for a story?

I think that's a pretty good idea for a story. One question though, when you said they had to get married, did you mean to eachother or other people? Because if they have to marry other people, then is the first one to get married get the throne, or maybe they get forced to get married to certain people? And you should think of what the symptoms of the decease should be, like big weird bumps all over the body, or weird internal bleeding, or maybe it's a decease that causes people to go crazy before they finally just die? I hope any of this helps with your story, good luck! I'd love to read it!