A standoff is underway between several members of John Wayne’s family — with his son and daughter battling each other over millions.

It’s all over The Duke’s estate — worth somewhere between $10 and $15 million … depending on which kid you ask.

In legal papers, filed Thursday in L.A. County Superior Court, John’s daughter Aissa Wayne claims she wants to sell her share of the estate — and another one of the The Duke’s kids, Ethan Wayne, is obligated to come up with a “fair-market” price to buy her out.

Aissa — along with several of Wayne’s grandkids — claim they believe the fortune is worth $15,400,000 … but Ethan only thinks it’s worth $10,704,000.

Now, Aissa — and the grand kids — want a judge to rule on the value of the estate … so they can get their money and move on with their lives.

– TMZ