What a world. After my last message I tried for a last time and then, BOOM! I made it! ... it was crazy difficult but I made it. And it was thanks to your tips.
A gambit to nullify lethal hits and the gautier knights were key to success. For me taking the city was impossible if Nader keeps sending Wyvern raiders, so I rushed to the ships, destroyed all anoying knights bow knights, then tanked the wyvern raiders little by little with Edelgard, crited Nader into space, killed some trash mobs aaaand... I teleported near Claude and that was everything. IN YOUR FACE, CLAUDE 😁 (OFC I executed him right away. He deserved it so much this time ...).
Anyway seems like my path in maddening continues all thanks to your knowledge. I might end up here whinning about chapter 15, but man, it feels good to end the nightmare that was chapter 14.
Thanks again.