For the old people in my family—Mummy, the aunties, Granddad—the accumulation of beautiful objects is a life goal.
 

Cadence, in Chapter 17, is critical of how the Sinclair family uses their wealth, which is to accumulate possessions. Penny tries to convince Cadence that beauty has a use, an opinion that Cadence rejects out of hand, failing to see that she values Gat for precisely this reason. Cadence also fails to see that these objects bring joy to the family, although she acknowledges that the possessions bestow status upon the Sinclairs. Like Cadence, Gat had been concerned about the extent to which the Sinclairs claimed ownership of the island, for example. However, Gat’s critique comes from a place of education, and it was phrased as an opinion or as a question, not as an accusation. 

You can get it, he said, about the ivory. 
One of his mottos: Don’t take no for an answer. 
It had always seemed a heroic way to live.

In summer fifteen, Cadence is heavily influenced by Gat’s socio-politically broadminded questioning, as this quote from Chapter 42 demonstrates. She begins to question the source of much of the Sinclairs’ collection of beautiful objects, particularly ivory, which is illegal because it is collected from species that are endangered. Cadence realizes that Harris uses his wealth and power to please his wife with what Cadence considers to be trivial objects. Harris, predictably, does not react well to her accusations, viewing her as a child who doesn’t understand how the world works. After this exchange, her understanding of her grandparents begins to change to a more negative appraisal. As a Sinclair herself, Cadence cannot escape the implications this interpretation has for her.

I see it for what it is, now. It is a house built on ashes. Ashes of the life Granddad shared with Gran, ashes of the maple from which the tire swing flew, ashes of the old Victorian house with the porch and the hammock. The new house is built on the grave of all the trophies and symbols of the family...

In Chapter 58, Cadence finally realizes why New Clairmont is so empty of all family memorabilia. Cadence was warned not to return to Beechwood Island for the sake of her mental and emotional health. Both her doctors and her mother feared that what she encountered there would trigger memories that were too difficult for her to face. But because she feels she must, she insists on going anyway. Not surprisingly, the changes are upsetting to her, particularly New Clairmont, which she understood as a remodeling. Her realization here is only the beginning of her understanding of all that is buried beneath those ashes.