If you unlink your characters, you can position them better before triggering the dialogue before the end fight. Sneak at the top of the stairs to have more room to move around. If you have a ranger there are places you can get for a high ground advantage for part one of the fight. If you do damage fast enough, you can skip the second part of the fight (ie Rain + Thunderstorm).
There should be end cutscenes on Youtube playthroughs. The details depend on choices and events earlier in the game, as well as the options at the end, so it may be easier to use something like the Cheat Commander mod before the final section to level up and boost attributes and skill levels, etc.
