In the history of Ilvermorny's founding, there had once been a pair of "twin wands." Both Chadwick and Webster used part of a Horned Serpent horn that Isolt had taken. Isolt ground the horn into powder and placed it in the wand cores. This method of making wand cores had originated with her; other master wandmakers used materials such as Unicorn hair and Dragon heartstring, which required no additional processing before being placed inside a wand.
When Gormlaith Gaunt came to their newly built school, the two brothers had also joined the battle. When the two wands faced a single enemy together, their power increased tenfold.
There was a limit to wand amplification and accuracy bonuses. Ollivander had never expected that the wand he had made would become what it was after being sold to Voldemort. Logically, it should not have possessed such great power.
There was a profession in the Wizarding World called wand tuning. They specialized in adjusting wands and optimizing their performance, so it was highly possible that Voldemort had modified and adjusted his own wand, making that yew wand better suited to him.
According to legends passed down through the Gaunt family, Salazar Slytherin had once made a wand from a red feather on a Basilisk's forehead and passed it down through the generations as a family heirloom.
It had always been merely an "exhibit" until Gormlaith Gaunt truly used it to carry out "Salazar Slytherin's plan."
Isolt had been part of that plan. Otherwise, no normal person would attack their own relatives, disguise it as an accident, and adopt someone else's daughter only to burden themselves.
The wand Isolt had stolen from Gormlaith was that wand made from a Basilisk feather. Thus, when Gormlaith spoke to it in Parseltongue, it "fell asleep" like a real