Two years after ROBERT F. KENNEDY Jr.’s estranged wife committed suicide, a family feud has erupted over his engagement to actress Cheryl Hines.

The two announced their betrothal while attending “Muhammad Ali’s Celebrity Fight Night” in Phoenix, Ariz., on April 29. But sources say Kennedy’s four children with tragic second wife Mary are considering boycotting the wedding, while his 86-year-old mom Ethel Kennedy is desperately trying to make peace.

“Bobby’s kids can’t stand Cheryl,” a pal told The ENQUIRER. “Whenever she’s at a family function, they call her ‘Buzzkill’ behind her back.”

Another insider added: “Even though their parents were estranged when Cheryl entered the picture, the children feel that her presence may have contributed to pushing their mom to take her life.”

Kennedy, 60, is the son of slain former U.S. attorney general Robert F. Kennedy and nephew of late President John F. Kennedy.

The environmental lawyer began dating Cheryl, 48, best known for her role in “Curb Your Enthusiasm,” in late 2010.

In May 2012, his estranged wife Mary, then 52, hanged herself on the grounds of the family’s home in Mt. Kisco, N.Y.

As The ENQUIRER has reported, the couple’s children – Conor, 19, Kyra, 18, Finn, 17, and Aidan, 12 – were “shattered” by their mother’s death and wanted nothing to do with Cheryl, despite her repeated attempts to woo them.

Sources say Kyra gave the “Suburgatory” star Cheryl the cold shoulder at her society debut in Paris last November.

In December, Kennedy’s two oldest children, Robert III and Kathleen, from his first marriage to Emily Black, also snubbed Cheryl at a Hollywood fundraiser, going out of their way to avoid sitting next to her.

Meanwhile, Kennedy has enlisted his elderly mother to help turn the tide of ill will, say sources.

“Ethel has tried to convince her grandchildren that this marriage will be good for them and their dad,” said the pal.

“She pointed out that even though Cheryl can never replace Mary in their hearts, they should be willing to at least give her a chance. After all, she’s going to be their stepmother whether they like it or not.”

The insider added: “Ethel realizes that the three oldest children can’t be expected to take much parenting advice from Cheryl. But she told the kids that it would be nice to have Cheryl’s support in other ways, such as attending milestones like their graduations, marriages and the like.

“Besides that, Ethel reminded the kids that Cheryl appears to make their father happy, and they should want him to have a relationship based on mutual love and respect.”

The just-engaged couple now hopes that Ethel’s intervention will convince his children to warm up to their soon-to-be stepmother.

“If the children boycott the wedding, it would be an absolute disaster,” said the pal. “But right now, Cheryl and Bobby can only hope that the kids will show up for their big day.”