The story of Mary Anerley opens in the year 1801, at Scargate Hall, "in the wildest and most rugged part of the wild and rough North Riding"; the first chapter being practically a prologue, which sets forth the strangely dramatic death of Squire Philip Yordas just after he had made a will disinheriting his son Duncan. Thus Scargate Hall, when first described to the reader, is the property two sisters, Philippa Yordas and Eliza Carnaby. Mr. Jellicorse, the family lawyer, comes by chance upon evidence of a fatal flaw in the sisters' title to the estate, and rides over to make them acquainted with this unpleasant fact.
In the sixth chapter of the book we are introduced to Anerley Farm, a place about a hundred and twenty miles from Scargate Hall, and the home of Mary Anerley. As Mary rides down the hollow of the Dyke on the same morning on which Mr. Jellicorse leaves Scargate Hall, she falls in with a man who is running for his life from other men who are pursuing him and shooting at him. Acting on the impulse of a moment, she shows him a place where he can hide. This man is Robin Lyth, who as a child was found washed ashore in a little cove north of Flamborough Head, and raised by foster parents. He is on the run from Captain Carroway, a coastguard officer. Love blossoms between Mary and Robin Lyth, but many obstacles interfere with true love's course.

Question: How do Philippa Yordas and Eliza Carnaby know each other?
Answer: They are sisters.
Alternative answer: They are sisters.