Julia Roberts’ marriage to Danny Moder may reach the breaking point – and this time it’s over his financially strapped dad, The National ENQUIRER has exclusively learned.

The “Pretty Woman” star got fed up helping retired film exec Mike Moder, 78, pay his mortgages, and after an ugly row, forced him to sell two homes, sources said.

Now Mike is estranged from his grandkids, and family members fear Julia, 47, and Danny, 45, are headed for a Thanksgiving showdown – when the long-festering family feud could blow sky high!

“The marriage is on the rocks,” claims the source. “There are a lot of issues with money.

“Julia said she doled out millions of dollars in mortgage payments for Mike. She helped him out for at least five years, and she got tired of footing the bill.

“It became a bone of contention between her and Danny, and Julia made (Mike) sell two of his homes – a house in Palm Desert, Calif., he had for over 30 years and a coastal retreat in 
Oregon.“That was almost a year ago. Afterward, Mike moved into a condo in Palm Springs.”

Mike, 78, started working as an assistant director in the early ‘60s, and climbed the ladder on the production side before retiring in the late ‘90s.Since his spat with Julia, Mike hasn’t seen her kids with Danny – 9-year-old twins Hazel and Phinnaeus, and Henry, 6 – for nearly a year.

Julia, who’s worth a whopping $140 million, has also helped out her hubby by kicking in money to boost his career as a cameraman, the source claimed.

“Julia’s done numerous projects with Danny, and each one turned into a financial nightmare,” said the source.

That includes her losing money on the 2008 indie film, “Fireflies in the Garden,” for which Danny was director of photography.

Meanwhile, the two also have butted heads over Danny’s family, with the trouble dating back to before they wed.

Several of Danny’s siblings blamed Julia for their mom Patti’s sudden 2001 heart attack death, claiming Patti was stressed over Danny’s extramarital affair with Julia while he was still married to makeup artist Vera Steimberg, the source said.

The bad feelings were reignited two years later when Julia skipped a memorial service for Patti due toAnd tensions between Julia and Danny’s sister Jyl escalated when Mike remarried, and Jyl blamed Julia for creating a media frenzy at the low-key family affair, calling her famed sister-in-law “Satan,” the source said.

What’s more, “Julia’s mom Betty has never liked Mike and she’s made it very clear,” said another source.

“All these problems could finally spell doom for Julia’s marriage come