This is way too many coincidences, we've long since passed into the territory of enemy action. Preliminary tactical thoughts:
Vanreir's power is the Unerring Blade of the Amarlt, their legacy briefly returned by some ridiculous combo platter of Soul Evocation bullshit that comes at ruinous cost. He relies on his connection to his sister and his father's soul. Blood ties, in other words. We should attempt to disrupt those with the Ring. He's also unfamiliar with his wounds, but Hunger's adjusted to lacking depth perception/coped with the injuries Vanreir just suffered for years. His Thrusts don't miss, but maybe they need to be aimed, and his aim is impaired. Maybe we can bait him into overcommitting or whittle him down with blade-winds at range?