OF COURSE, Winter didn't report it to his father yet because he hadn't gathered enough evidence to say that they were being brainwashed by his stepmother using Moonflowers.
So he installed a spying device on his room that he covered with his ice to hide its presence. One of his birth mother's major businesses was to create device from unique spirit stones that could only be found in Mount Solace– the mountain owned by the Prescotts.
The kind of device that he used was the spirit stone that could record voices. That was the most advanced spying device that their family possessed.
And so, he recorded his stepmother's voice for the past two weeks.
That was when he realized that his stepmother talked about nothing else but how awful his birth mother was.