UPDATED with Viacom response: Viacom CEO Philippe Dauman’s case to overturn a decision to dump him from Sumner Redstone’s family trust and the National Amusements board is “legally insufficient” and should be dismissed, Redstone’s lawyers told a Massachusetts court today.

Dauman and Viacom director George Abrams asked the state Probate and Family Court to find that Redstone, 93, is mentally incompetent and being manipulated by his daughter, Shari. They say that she wants to control her father’s media empire. When he’s deemed unable to manage his affairs, a seven-member trust will vote his 80% stake in National Amusements, which owns 80% of the voting shares in Viacom and CBS.

But Redstone’s motion to dismiss says that his family trust lays out two conditions for finding him incapacitated, and neither has been met. He’d have to be assumed competent unless found otherwise by a “court of proper jurisdiction” — which they say would be in California, where he lives — or by three doctors.

Since neither has happened, Dauman and Abrams “do not, and cannot, properly invoke either of the Trust’s exclusive grounds for deeming Sumner incapacitated,” the filing says.

The duo’s argument that Shari is manipulating her father also falls, Redstone’s lawyers say. The law governing “undue influence” is designed to protect a trust’s beneficiaries from an “unnatural disposition” of assets — and that hasn’t happened.

“Absent a disposition of trust funds or property, there can be no common law claim of undue influence,” the filing says. It adds that “Sumner’s exercise of his right to remove and replace two of the seven Trustees who administer the Trust was decidedly administrative, not dispositive, in character.”

Redstone wants a California court to validate his decisions to oust Dauman and Abrams — specifically, state Superior Court Judge David Cowen, who last month dismissed a separate case to have Redstone declared incompetent. Cowen has scheduled a hearing on the new matter for October 18.

The motion in Massachusetts includes a “declaration” from Redstone, dated today, noting that it’s made “under penalty of perjury,” and with a diagonal line as a signature.

It says he understands that Dauman and Abrams “contend that I was unduly influenced by my daughter to remove them as trustees and directors. That is offensive and  untrue. I want that dispute, and any challenge to my competency, to be decided in Los Angeles, California. I object to having any such challenge decided in the courts of Massachusetts or otherwise outside of my home state of California.”

Viacom says that the motions to dismiss come from “Shari Redstone and the lawyers hired for Sumner.” It adds that the arguments “represent continued efforts to avoid a fair inquiry into Sumner’s well-being and how various documents came to be. The facts will only come out through discovery on an expedited basis. We are urging the court to allow the inquiry to proceed as quickly as possible.”