Agents are independent contractors who hang our licenses with a broker. The broker actually owns the listings we go out and get. So, yes, you do have to share them with your broker. Regarding the other agents in your office, they also are operating under the auspices of your broker, so as part of that brokerage it would seem you can't pocket these listings. I see from your zip code that you are in Park Slope, which is where I live and sometimes sell, though my office is in Manhattan. There are still Mom and Pop shops on 7th Ave. that are not part of REBNY. If you are not part of REBNY, and since we don't have a real MLS in NYC, you don't have to share it with the rest of the brokerage community. If you are part of REBNY you have to put it into the ROLEX system within 24 hours.
My own personal view is if you are not putting your listings out there to the entire brokerage community, you are not serving your seller well, as your fiduciary repsonsibility is to get that property sold in the least amount of time for the most money, which can only be done by co-broking. Also, it must be very lonely doing business that way. I have made many great friends in the brokerage community through co-broking our deals, whether I am representing the buyer or the seller. And in my present and past company, the comradery and collegiality is/was a big part of why I love what I do.
Halstead Property, LLC