As the estranged daughter and grandchildren of Saints owner Tom Benson seek to have him declared mentally unfit, a second drama is playing out that also has the potential to undermine his effort to wrest away future control of his sports franchises and award them to his wife.

At issue is whether Benson has the ability to remove the Saints and the Pelicans from the trusts that hold them, which were set up within the last five years by Benson for his now-estranged daughter, Renee Benson, and her children, Rita LeBlanc and Ryan LeBlanc.

Such trusts are designed to protect heirs from having to pay estate taxes. Because the trusts are irrevocable, Benson may not, for instance, add his wife as a beneficiary and remove his daughter and grandchildren.

Records in the lawsuit filed by Benson’s heirs Thursday indicate that Benson last week attempted to remove the teams and other assets from the trust and replace them with an unsecured promissory note for $427 million. It’s unclear from the lawsuit whether that was the only asset Benson pledged.

That move, at least temporarily, has been blocked by a Benson-appointed trustee, Bobby Rosenthal. A letter dated Monday, signed by Rosenthal’s lawyer, says Rosenthal determined it would not be “prudent, nor an appropriate trust investment” to carry out Benson’s request.

According to the lawsuit filed by Benson’s heirs, that’s because Benson grossly undervalued the two sports franchises he sought to remove from the trust. The lawsuit says Benson proposed valuing the teams as follows: $63.5 million for the Pelicans, and $351.4 million for the Saints.

Forbes magazine recently put the two teams’ value at $650 million and $1.1 billion, respectively, the filing notes. That’s more than four times what Benson apparently estimated their value was.

The documents in which the lower valuations were apparently asserted by Benson were not made part of the lawsuit.

Paul Cordes, the lawyer for Tom Benson who sought to arrange the transfer, referred questions to Saints and Pelicans spokesman Greg Bensel, who declined comment.

Rosenthal and his attorney, Kevin Kennedy, did not return telephone messages seeking comment.

The standoff over the trust swaps could throw a monkey wrench in the plan Benson announced Thursday morning to give his wife, Gayle, control of his sports empire upon his death, instead of Rita, who had been seen as his successor. The proposed trust transaction underpins the plan to shift Benson’s considerable wealth to his wife.

According to several experts on estate planning interviewed Thursday by The New Orleans Advocate, the trusts in question appear to be what are often known as “intentionally defective grantor trusts.” Despite the odd name, they are perfectly legal.

Very wealthy people — typically those with $11 million or more in net worth — often set up irrevocable trusts for their heirs to shield them from having to pay estate taxes on their inheritances. Normally, the grantor — in this case Benson — may not touch the assets placed into these trusts.

But with grantor trusts, the grantor pays all taxes on income generated by the trusts as a way of further protecting his heirs’ inheritance. In exchange for that, the grantor is allowed to remove assets from the trust, provided he replaces them with an asset of equal value.

It’s up to the trustee — in this case Rosenthal — to ensure that the replacement asset is worth as much as the asset being removed. If the trustee fails to do so, he could be sued for breach of fiduciary duty by the beneficiaries: Benson’s now-estranged heirs.

Benson apparently believed there would be no problem with his proposed swap.

In a Jan. 12 letter, Benson’s attorney Cordes told Rosenthal that Benson was taking back the teams, car dealerships and banks held in the trust “effective immediately” in exchange for the $427 million promissory note. It’s not clear whether any other assets are pledged.

“I think it is clear from the trust provisions that Mr. Benson has the unrestricted right to do what has been set forth here, but to avoid any confusion on the matter, the removal of the assets is effective immediately, and he will act accordingly,” Cordes wrote.

Cordes suggested that he, Rosenthal and another Benson attorney Phil Wittmann meet in San Antonio to discuss the change, along with Renee Benson and Rita and Ryan LeBlanc.

The response from Rosenthal’s lawyer said Rosenthal did not believe the transfer would be “prudent” or “appropriate.” It also said Rosenthal would need copies of appraisals of the assets and maybe even would conduct an appraisal of his own.

“…The notion that an exchange has occurred is incorrect,” Kennedy wrote. “Until an exchange occurs, no trust assets have been removed and replaced. Any representations to third parties that trust assets have been replaced by Mr. Benson would be materially false.”

Several things could happen next, according to experts. Benson could propose swapping another asset for the teams, if he has one, or he could secure his promissory note with another asset. If he has no other assets that are valuable enough, he “could grant some security interest in the franchise,” said Rebecca Hinton, an expert on trusts and other financial matters at the law firm Phelps Dunbar.

If Rosenthal remains unsatisfied with Benson’s proposals, he could continue to negotiate with Benson — perhaps by hiring outside appraisers. If he is still uncomfortable, Rosenthal may ask a judge to sort out the mess, which would protect him from any claim of breach of fidiciary duty.

Benson, meanwhile, could seek to replace Rosenthal as trustee.

“With these kinds of dollars at stake, there’ll be fights over everything,” predicted Joel Mendler, an expert in estate planning at the law firm Baldwin Haspel. “The only ones who will win will be the lawyers.”

Follow Gordon Russell on Twitter, @gordonrussell1.