...As in the threads on the stud are stripped and the nut spins in the same place but the stud stays stationary?
If that is the case, try wedging a thin flat bladed screw driver between the cone washer and the nut to give some "outward" force on the nut as you try to spin it off. You want to force it outward so it can hopefully pick up a remaining thread and come off. Once it is off, you will definitely need to replace the stud as you won't get it tight enough again to actually put force onto the cone washer.
Double nut one of the other studs and remove it. See if you can thread it in the other hole. Might as well order a whole set for both hubs including cone washers. They can get mangled if you hit it too hard with a Brass hammer or if you lose a cone.
You also might as well post some pics of your spindles too. Save everyone another thread about “how do my spindles look”.