I wouldn't try it, personally. That water change schedule might work in a 14g tank with one axolotl, but I doubt it would work for two.
As Alkylhalide and Quentari said, the absolute minimum size for two axolotls should be 20 gallons, but preferably larger. Keep in mind that the furniture in an aquarium (hides, plants, substrate, etc) take up water volume that can be used to help dilute toxins in the water. The greater the water volume, the better.