Kyle Richards' ongoing feud with sister Kathy Hilton has just gotten even more intense.

Did Kathy Hilton & Kim Richards Snub 'RHOBH' Kyle On Her Birthday?

After feuding during filming on The Real Housewives of Beverly Hills, the two womens' tensions were rebooted when their husbands, Mauricio Umansky and Rick Hilton, were each given the listing for the upcoming sale of the Playboy Mansion.

"Kathy and Kyle are still not on speaking terms," a source told Radar Online on Saturday. "These two sisters are so stubborn that neither one is going to back down and reach out to the other one."

Report: What Does 'RHOBH' LIsa Rinna Really Think Of Kyle Richards' Ongoing Family Feud?

After working with Kathy's husband, Rick, for years at Hilton and Hyland, Umansky branched out, and started his own firm, The Agency. Ever since, things between the two men, and their wives, have been extremely strained.

"The sale is strictly business and it isn't technically split, it is whichever place actually sells it gets the commission," an insider told Radar. "No one actually met with Hef. The Playboy people took meetings with several companies and decided to hire two because it is a big transaction."

However, that doesn't mean Hilton and Umansky are working together -- and it also doesn't mean they will be splitting the commission. As the report revealed, the commission will go to whichever company finds a buyer.

"Rick and Mauricio don't have to interact," the source added.

For more of Kyle Richards and her family, tune into The Real Housewives of Beverly Hills season six, airing on Tuesdays at 9 p.m. on Bravo.