For nearly two years, Madeline Cuomo quietly worked with grass-roots activists to help smear her brother’s accusers. He was “seeing everything,” she told his defenders.

The menacing posts began cropping up on Twitter last September just hours after a former aide to Gov. Andrew M. Cuomo of New York sued him over sexual harassment claims.

The tweets attacked the aide, Charlotte Bennett, in starkly personal terms. “Your life will be dissected like a frog in a HS science class,” read one of the most threatening, which also featured a photo of Ms. Bennett dancing at a bar in lingerie.

The post was part of a thread written by Anna Vavare, a leader of a small but devoted group of mostly older women who banded together online to defend Mr. Cuomo from a cascade of sexual misconduct claims that led to his resignation in August 2021. But it turns out, her tweets had secretly been ordered up by someone even closer to the former governor’s cause: Madeline Cuomo, his sister.

In the hours before the posts went live that morning, Ms. Cuomo exchanged dozens of text messages with Ms. Vavare and another leader of the pro-Cuomo group We Decide New York, Inc., pushing the activists to target Ms. Bennett, one of the first women to accuse Mr. Cuomo of sexual harassment. She appeared to invoke her brother’s wishes.

“Good Morning Just spoke and he thinks a distraction could be helpful today,” Ms. Cuomo wrote in the private texts reviewed by The New York Times. She suggested posting “photos of Charlotte In her sex kitten straddle” taken from Ms. Bennett’s Instagram account, potentially alongside more “austere, professional” ones of loyal Cuomo aides.

“No respectable woman would EVER pose like that,” Ms. Cuomo added.

She went on: “Bimbo photos.” “Really despicable.” “Unsophisticated girls.”

Far from an isolated episode, the unvarnished exchange is part of a trove of more than 4,000 text messages, emails and voice memos between leaders of the group and Ms. Cuomo shared with The Times this summer. Together, they provide unusual insight into how far members of one of America’s most storied political families were willing to go to rehabilitate a fallen Democratic scion and humiliate those they believed had wronged him.

Made up almost entirely of women inspired by Mr. Cuomo’s handling of the Covid pandemic, We Decide New York rapidly joined forces in spring 2021 to defend an increasingly isolated governor as traditional allies abandoned him. The group swarmed his critics on social media, sold Cuomo swag and pushed for due process.

But four of the group’s current leaders said in interviews that even as their work appeared organic to the outside world, Ms. Cuomo, 58, began privately exerting control. Starting just weeks after the group was formed, she steered its volunteer activists — many in their 50s, 60s and 70s — to prop up her brother and hound his accusers ever more aggressively.

It is unclear how much Mr. Cuomo knew about his sister’s efforts. He does not appear to have directly communicated with the supporters. But in the messages reviewed by The Times, some of them sprinkled with typos, Ms. Cuomo repeatedly stated that she was keeping her brother updated and acting at his direction.

“I just hung up w A again and he wants you both to know how much he appreciates ALL your hard work,” Ms. Cuomo wrote last September. A few days later: “He’s seeing everything.”

Ms. Cuomo was adamant her role be hidden. She repeatedly asked her interlocutors to delete messages. And when a reporter for The Times called some leaders of the group for an earlier article, Ms. Cuomo instructed the women to falsely claim they had no contact with the Cuomos, according to Sandy Behan, the founding president of We Decide.

Ms. Cuomo, in a statement on Monday, acknowledged her involvement with the group, saying she was focused on “protecting my family” but insisted that her brother played no role. “I acted on my own with the women of WDNY, without his involvement in any way,” she said. “Unfortunately, due to internal dissension, the group fractured, and I haven’t worked with the group since.”

Mr. Cuomo’s spokesman, Rich Azzopardi, also sought to distance the governor from his sister’s efforts.

“The governor does not personally have nor does he follow social media accounts, and he was not directly or indirectly involved in these online efforts,” he said. “When he’s had something to say, he has not held back from doing so publicly.”

Ms. Behan, 71, said she and others were awe-struck after being contacted by Ms. Cuomo and were eager to help her with what they believed was a shared — if sometimes unsavory — mission. But by late last year, the relationship had imploded around a proposed documentary project and Ms. Cuomo’s intensifying demands.