Advice?

Use History as your guide. Surely Omeria isn't the only continent in your fictional world; probable there are other Kings, Queens, Emperors, Sultans, etc, etc.

Political games, especially of the medieval sort, are often a sort of 'wheels within wheels' affair: the royal family's assassins may all be Omerian, but maybe the (or one of the) forces behind the assassinations are not native to Omeria. A slighted religious leader? A foreign distant relative to the royal family looking to power grab, or simply respond to their distant family being murdered? Maybe the Omerian royals wronged a powerful merchant guild? Or worse, didn't pay their creditors? 

(To say nothing of typing in 'campaign ideas', or 'roleplaying ideas.' A lot of tabletop RPers use the internet as a means to share ideas, and they're a great resource for roleplayers like us on the Guild.)

Countless options. Options easily found in our real world history book (also other works for fiction, not just GoT), stories just waiting to be discovered and re-imagined for your setting.

Hope that helps! <3