The supermodel spends July 4 at the singer's house, while Peter Cook goes sailing with son Jack

By Charlotte Triggs
Updated July 05, 2008 06:45 PM

Christie Brinkley spent the Fourth of July “blowing off some steam” at ex Billy Joel’s Sag Harbor, N.Y., house, a source tells PEOPLE.

Brinkley, whose ugly divorce from Peter Cook has been heating up in court, arrived with daughter Alexa Joel, 20, and “seemed good,” says a friend of the supermodel’s. “She was just blowing off some steam, being with family. It was just a relaxing little get-together. Nothing special. Just what everyone does on the Fourth.”

Another onlooker says Brinkley, Alexa, Billy and about a dozen friends “were having a blast,” eating barbecue ribs and corn and sipping white wine.

At one point Alexa dropped her first plate of food – “they were all laughing about that,” says the source.

As for Brinkley, “she was hugging the kids there, they were all laughing and eating. They seemed really relaxed.”

The day before, Brinkley also surrounded herself with family and friends, enjoying a midday lunch with her son Jack, 13, and a girlfriend at Gosman’s Dock in Montauk, N.Y.

“Christie looked beautiful in a white floral sundress, but she wasn’t exactly upbeat,” says a fellow diner. “Maybe just a little tired but she seemed relaxed – kind of just getting away from it all and having a nice lunch.”

“She seemed OK, said hi to a few friends,” says the source. “She was very pleasant – calm and casual.”

Meanwhile, Cook spent the holiday with his 13-year-old son Jack and girlfriend Suzanne Shaw. After picking up Jack from Brinkley’s house, the trio went for a ride on Cook’s boat, The Sweet Freedom.

“He seemed fine, relaxed,” says an onlooker at Island Surf shop in Sag Harbor, where Cook stopped in with Jack to pick up T-shirts and “stuff for camp.” Adds the source: “He’s always in here with his son. He’s a good guy – and a great dad.”