Both men will work for Andres Anker, a portfolio manager at SAC who left in June for Millennium after nearly 10 years under Cohen, according to people with knowledge of the firm.
Jonathan Gasthalter, a spokesman for SAC, and Carly Westerman, a spokeswoman for Millennium, declined to comment. Chentsov, Falconi and Anker did not respond to requests.
(Read more: SAC Capital looking at just managing insider capital)
The moves aren't a major change to either firm but underscore the upheaval SAC faces since running into trouble with regulators.
The U.S. government filed a criminal fraud charge in July against SAC for allegedly fostering a culture of insider trading. The firm has contested that and related charges.
Millennium has more than 1,300 employees and 140 specialized trading teams managing $18.5 billion in assets. And SAC runs almost $14 billion as of July 1 using about 1,000 employees, including 125 long-short equity portfolio management teams plus an undisclosed number of quantitatively oriented PMs.
The Millennium International Fund is up 7.13 percent through July, according to a person familiar with the returns. SAC has gained more than 11 percent through August. SAC's assets under management will likely fall to between $9 billion and $10 billion--mostly Cohen's own money--by early 2014 as investor redemptions are processed.
SAC recently moved to retain investment staff, increasing base pay to a minimum of $300,000 in 2014—up from $200,000 in 2013--and adding an incentive bonus of 3 percent for work this year, according to a recent CNBC report.
Several departures preceded those pay increases.
In August, SAC cut one unit, Parameter Capital Management, run by portfolio managers Glenn Shapiro and Anil Stevens.
Stevens is leaving to launch his own fund, according to Reuters. The move was planned before the Securities and Exchange Commission filed charges against SAC.
(Read more: SAC Capital pleads not guilty to all charges in court)
Many investors have redeemed their money from SAC in the last year. Accordingly, SAC cut about a dozen people on its marketing and investor relations staff in August.
Those departures included Chris Rae, a director who had been with the firm since 2008. Rae did not respond to a request for comment.
Headhunters say it makes sense for SAC employees to consider leaving the firm.
"It would be clearly sensible for anyone at SAC to be exploring other options right now and to be putting their candidacy in early for 2014 hires," said Bob Olman, founder of hedge fund-focused recruiting firm Alpha Search Advisory Partners.
—By CNBC's Lawrence Delevingne. Follow him on Twitter @ldelevingne. CNBC's Kate Kelly contributed to this report.