You address everyone before the Wild Hunt attacks. Ciri explains how the Wild Hunt chases her, and a counter-attack strategy is agreed upon by the assembled friends. Preparation is required. Choose any talking point you wish.
You will ride out to attack foes in the woods with Lambert and Letho. Lambert’s dimeritrium bombs, and the Yrden Sign, should help close the navigator portals the Wild Hunt will use. Yennefer hands out amulets that will make all of the hunting party invisible. Triss is to provide potent fire magic when called upon.
You agree that Ciri is the most important, after which Roche offers to dig some trapping pits to waylay the Wild Hunt. Zoltan offer his sticky, flammable Mahakaman mix, and Ermion will make use of the natural gas pockets the keep sits on, but only if you invited these fellows along for the battle. Vesemir mentions the workshop and laboratory, and that one type of weaponry can be crafted at each location. Vesemir will continue brewing potions at the laboratory. Or Eskel can prepare more witcher traps. Make your choice:
Choose the potion, and you receive Superior Swallow. If you completed Secondary Quest: Following the Thread with Lambert, you also receive Fortified Rafard’s Decoction; both helping you survive the battle to come.
Choose traps, you will see traps appear on all the yards of Kaer Morhen. When a foe walks into these traps, they explode. Therefore the choice between potions or traps is a tactical one; are you better at dealing a lot of damage (choose potions) or receiving a lot of damage (choose traps)?
Vesemir wants to fix the breach in a wall, but the same workshop tools are needed to clear a cave in at the armory, where some choice swords are available. Make your choice:
Choose to patch up the wall, and Savolla’s breach (from Witcher 1) is closed up, and the final stand-off has one fewer wave of enemies entering Kaer Morhen.
Choose to clear the armory, there are some scenic changes and you gain access to a locked part of Kaer Morhen, where the armory was. Here you can obtain a superior silver sword and all the witchers in this fight receive weapons that deal more damage. The decision here is also a tactical one: Do you prefer to have more of the Wild Hunt to kill, but with a better sword, or fewer enemies and a lesser weapon (unless your own crafted sword is preferable...).
The preparations are completed, and Lambert readies for combat. Join him when you’re ready. On the way, you speak to Ciri, impressing upon her the need to keep her safe. Then head west, out of the keep. Your comrades take up their positions. The Wild Hunt arrives, and Yennefer conjures her protective shield.