“Our house in Sherman is about openness,” the younger Mr. Wildenstein says of his estate.

He said Migdale was in shambles when his family purchased it. They reimagined the entire home, starting with limestone salvaged from an estate in Brittany to cover the walls and floors in the entrance and hallways. They commissioned custom wood doors in keeping with the home’s period architecture. They ripped out modest stone fireplaces, moved them to the staff quarters and installed ornate French marble mantelpieces. They imported an entire wooden bar from an 18th-century pub in England for their game room. They covered the walls of the grand 58-foot-long living room with yellow Coraggio silk-velvet fabric and removed a massive pipe organ from the same room, which was donated to a church in Wilmington, Del. The mansion’s air conditioning is now cleverly housed within the old organ pipeways.

Each of the four Wildenstein children were allowed to select a style for their bedrooms, resulting in some eccentricities. One bedroom is covered in raspberry-and-white padded fabric. Another bedroom looks like a chalet in the Courchevel ski resort, complete with a preserved tree—bark and all—that forms a spiral staircase to a loft.

Where the aviary once stood, there is now a grand terrace that looks over a lawn large enough for a nine-hole golf course. They dynamited down to the bedrock to create that terrace—and the massive amenity floor below, which features a home theater, 43-foot swimming pool, gym, his-and-hers saunas, treatment rooms and a 5,000-bottle wine cellar.

The Wildensteins moved dozens of mature trees to improve views. They built a tennis court and two ponds with picturesque islands. They planted a large garden to supply organic vegetables for the family. To keep away deer from heavily trafficked areas, they created grazing fields and orchards. They even transformed an old sheep barn into a Medieval-style, thatched-roof barbecue house with a long communal table and spits large enough to roast an entire pig.