The Noble House of Wachter

Fiona Wachter shared this information after helping the party defeat the Gllows Speaker and rescue her daughter Stella from the ethereal plane. She made the connection when the Gallows Speaker refer to itself as Leo Dilisnya...
Her ancestor, Lady Lovina Wachter nee Dilisnya, came to Barovia shortly after Strahd von Zarovich settled it. For her loyalty, she received deeds to land and estates, as well as a Barovian title with Strahd as her liege-lord.
Lovina, an amateur historian, wrote The Noble House of Wachter to document her new family's history, which allegedly dated back to the days of Old Zarovia, long before Barovia was founded.
Once Lady Wachter has located the proper page, you are read the following passage from Lovina's book, titled only "The Wedding" and written in erratic, jagged pen-strokes at odds with the clean, elegant script of the remainder of the book:

The wedding of Prince Sergei von Zarovich and Tatyana Federovna began with good cheer, but ended in madness and blood. Prince Sergei was found dead in his chambers, his bride-to-be rumored to have cast herself from the overlook in despair.
Though no suspect was confirmed, Leo Dilisnya—my own kin—led a treacherous uprising against Lord von Zarovich, abetted by a score of castle guards. When I sought to mediate, they turned upon us, slaughtering Vladislav and his mother and confining us within the confines of the kitchens.
It was only by some miracle that Lord von Zarovich emerged unscathed from their assault. Now possessed with an unearthly power, he smote the traitors and drove Leo himself from the castle.
In his escape, I saw Leo's face contort with hatred and disgust. "Blood-traitor, I name you, Lovina," he swore, "for your allegiance to the beast who abandoned Reinhold to his fate." He renounced our bond, proclaimed I was no longer of House Dilisnya, and vowed that he would one day expunge the Wachter blight from the valley—once and forevermore.
I know not what has become of him. He is gone from the Pillarstone now, and though more of the treacherous guards return in caskets to the castle each day, his face is not among them. But each night I hear his voice in my nightmares, I know he yet lives—and dread the occasion of his return.

The remainder of the book is concerned with genealogies, family legends, and notable figures in House Wachter's pre-Barovian history, with little relevance to Strahd.
Lady Wachter  shares that, according to the book, Vladislav was a Wachter and Lovina's husband. She isn't sure who Reinhold is, however, and doesn't know any more relevant information about Lady Lovina Wachter, Leo Dilisnya, Sergei von Zarovich, or Tatyana Federovna.