Michael S. Ross, attorney for Francis X. Morrissey Jr., said Monday he received a telephone call from the Manhattan district attorney's office informing him of the indictments.
"He has been indicted," Ross said when asked about Morrissey.
He said the charges had not been unsealed and he did not know what they are.
A law enforcement source told the New York Daily News the two will be charged with grand larceny and forging Astor's signature on a will that gave them control of her fortune.
The New York Post reports amendments to Astor's 2002 will shifted much of her fortune away from her favorite charities and directly to her son, Broadway producer Anthony D. Marshall.
Marshall and Morrissey had been accused in a civil suit by Marshall's son of misappropriating cash, real estate, securities and other property belonging to the socialite, who died in August at age 105.
Marshall's son, Philip, prompted the criminal investigation last year after he accused his father of neglecting Astor's care and stealing her money.
"It's hard to express my feelings at this moment," said Philip Marshall told the Daily News.
A Manhattan grand jury heard testimony for almost a month about the district attorney's investigation of how Marshall and Morrissey managed Astor's estate.
Ross said Morrissey was out of town Monday and would return later in the week. He said he thought Marshall, 83, would be arraigned Tuesday.
Marshall's current lawyer, Kenneth Warner, did not immediately return a telephone message seeking comment Monday. Prosecutors declined to comment.
Philip Marshall's spokesman Frazier Seitel said his client had testified before the grand jury. Seitel said banker David Rockefeller, who had spoken out on behalf of Philip Marshall's side of the dispute, had not.
Astor, known for decades as the grande dame of New York society and philanthropy, gave away nearly $200 million to institutions such as the New York Public Library and Carnegie Hall and to other causes.
In the final year of her life, the nasty family feud over her care was splashed all over the city's tabloids - including allegations that she was forced to sleep on a couch that smelled of urine while subsisting on a diet of pureed peas and oatmeal.
One of the tabloids Tuesday morning ran the headline "Crook Astor."
Anthony Marshall had agreed to a settlement before Astor died that made Annette de la Renta, wife of fashion designer Oscar de la Renta, Astor's guardian. After Astor's death, de la Renta and JPMorgan Chase challenged the validity of Astor's final will and suggested that Marshall might have misused $18 million of her fortune.
Anthony Marshall is a former diplomat and producer who won Tony awards in 2003 and 2004. He has denied allegations that he abused his mother's trust - saying that he cared about her more than anyone else.