When RJ King, Tripp Swanhaus and Carole Radziwill decided to share a miniature goldendoodle last year, friends discouraged it and scratched their heads. They worried that a puppy would become neurotic or confused about which of the three apartments on different floors in the SoHo building where they live would be her real home. And who would be the real boss? Mr. King, a model? Mr. Swanhaus, a marketer? Or Ms. Radziwill, a Real Housewife on TV and real author?

“But it has turned out that she knows her place in the world,” Ms. Radziwill said.

“And she isn’t needy, because what would she need?” Mr. King said.

“She gets to live in three one-bedroom apartments instead of one,” Mr. Swanhaus added.

Ms. Radziwill now has a boyfriend, Adam Kenworthy, a vegan chef who is fond of the dog too.

“I like her soft and fluffy, so I give her baths,” he said.

The other night, the “co-parents,” as they call themselves (never owners or masters), were lounging in Ms. Radziwill’s well-appointed living room, which included one very important and now shredded French couch. It was previously owned by Lee Radziwill, Carole’s mother-in-law from her marriage to Anthony, who died in 1999.