The Brothers Zeckendorf are on a roll.

“Yes, it’s fair to say that we’re optimistic,” Arthur Zeckendorf said. “Things are going well. There have been no shortages of setbacks, but we’re very resilient.”

Older brother William Lie Zeckendorf, also co-chairman of Zeckendorf Development LLC, added: “In New York, your name counts only as long as you’re in business. ‘New York’ and nostalgia don’t go together. We’ve found that this is not a sentimental town when it comes to doing business. You could have a father and grandfather who were giants of the game, but you’ve got to prove yourself in this city.”

The Brothers Zeckendorf, who joined their legendary father, William Zeckendorf Jr., after their graduation from Tufts University in the early 1980s, seem to have more than proved themselves.

For example, they have just set the North American record for condominium sales. More than two-thirds of the high-luxury apartments at 15 Central Park West, the 43-story neoclassical Manhattan complex designed by Robert A.M. Stern, have been snapped up since September, fetching $1.2 billion — and counting. A majority of the buyers are New Yorkers.

They also have completed 14 years of being partners in an independent real estate and development business where their signature has been putting up residential buildings at prime locations.One such project was 515 Park Ave., where the brothers raised a 43-story limestone and beige-brick tower, the tallest residential building on Park Avenue.

They have even moved out of the large shadow of their father.

It was he who built the Columbia, at Broadway and 96th Street, a condominium that drew much applause for its design. It was he who built the sprawling complex in Union Square known as the Zeckendorf Towers. It was Mr.Zeckendorf who built Worldwide Plaza on Eighth Avenue, in effect extending the rehabilitation and renewal of Times Square.

Perhaps even more than from the shadow of their father, who lives in retirement in New Mexico, the Brothers Zeckendorf have moved out from under the shadow of their grandfather, William Zeckendorf. He is widely regarded as the man who changed New York’s skyline, if not landscape. It was he who built or owned Chase Manhattan Plaza and the Chrysler Building in Manhattan, and the huge shopping complex on Long Island, Roosevelt Field. It was Zeckendorf who raised the Mile High Center in Denver.

It was Zeckendorf who bought 17 acres of land along the East River to develop a large shopping and residential complex, but then decided the land could be better used for the world headquarters of the United Nations, then in its infancy. For what was then considered a pittance, he sold the property to John D. Rockefeller Jr., who in turn gifted it to the U.N.

As it turned out, that transaction yielded unexpected benefits for Zeckendorf. His son, William Jr., had a blind date with the daughter of the man who was then the U.N.’s secretary-general, Trygve Lie of Norway. He fell in love with Guri Lie, who later bore him two sons, William and Arthur.

Such family history crops up frequently in conversation with the brothers.

“They were such great visionaries of their time,” Arthur Zeckendorf said of his forebears.

“We learned from their lives the meaning and value of responsibility to the community — and the importance of creativity,” William said.

The brothers also learned from their demanding father that he would cut them little slack because they happened to be his progeny. They would start their workdays at 7 a.m., and usually work until midnight. Although each brother was given his own set of specific projects, the father had the final say. But they were witness as Mr. Zeckendorf moved from converting hotels into residences to becoming one of the biggest developers in New York.

“We learned how to deal with local neighborhoods and community boards,” Arthur said, citing one instance when he helped transport a neighborhood garden from a site that the Zeckendorfs were developing to Riverside Park, where it flourishes to this day.

“He taught us everything we know,” William said. “He left us with an extraordinary education and value base. The level of knowledge, the hard-won business experience, the ability to figure out opportunities and make the best use of them — we would never have received this training anywhere else.”

At the same time, Mr. Zeckendorf leaves the impression that had he and his brother continued working with their father, their careers might have moved at a different pace.

“It would have been very different had he still been in business,” he said.

The father retired in 1992, and the brothers started on their own.

It was not an auspicious time to be independent in the real estate industry. The market was so troubled that the brothers were forced to explore areas beyond residential real estate, such as the retail business.

“We were trying out everything at that point,” Arthur said.

“It was amazing that we kept up our optimism,” William added.

Their optimism was enhanced by the acquisition of Terra Holdings, the brokerage Brown Harris Stevens, and Halstead Properties.

“From there onward, our deals began going way up,” William said.

He said they typically do two or three big deals in a year — and that for every deal they pick, they consider 20.

“There are a lot of big things out there that you want to do,” Arthur said. “But you have to let your ego take a back seat, and you have to let the analytical process take over.”

That process has resulted on a focus on the high-end residential market. Because interest rates are steadily going up again, it’s a difficult market in which to move these days, and the brothers are understandably reticent about speculating too much other than to say that they plan to continue concentrating on New York.

Neither do they do much looking back.

“When a project is done, it’s done,” William said. “I rarely dwell on the past, on projects that we might have missed out on.”

“There’s always pressure to make that next deal,” Arthur said. “I find myself asking, ‘Are we missing anything? Are we active enough?'”