Chill_ean_GUY
This is exactly what I wanted to see not sure what Cersei expects from this meeting Wilhelm will most likely not cheat and I'd she does it be obvious the child is Prussian when it grows up. Also this tournament could be used to demonstrate military strength and their advancements. Ik they are sticking to swords but If I remember you mentioned flintlock but them not being in favor or something. Maybe they can make valyrian flintlocks to make them usable. He can promote them as a gentleman's dueling weapon kinda like how they were initially viewed as. Please take my suggestions with salt as this is your story and I'm an uninformed dummy.
wait flintlock, is it like a gun right if the prussian create something like that. they must protect its's secret because many people will try to learn that weapon and it will be a headache to the prussian if their enemy manage to recreate it. especially tywin that guy will do everything to learn that weapon .
In this case, leave it as in the story, send some spies to the iron islands to find out when the attack will take place and let him defeat the Lannisters, thus burning Tywin's commercial fleet and ending his dreams of getting rich through trade, and after the grayjoys are defeated at Guardamar along with the royal fort, finish off the rest of the ships and accompany Robert in an attack on the Iron Islands with all the lords of the 7 kingdoms, thus showing their power.
In my opinion, after reading and re-reading about the Greyjoy rebellion, they attacked Lannisport and Guardamar, because they were the closest enemies and represented the greatest threat to them in the short period, the reason they didn't attack the countryside is because of the islands shield and distance, because as soon as the attack on Lannisport occurs, the countryside would know about the possible attack and would defend itself better and immediately after setting Lannisport on fire Balon declared himself king sending letters to all the houses of the 7 kingdoms, and soon after sent His son attacked Guardamar which ended in failure, leaving him with only one full-strength fleet to use.