Articles about two dimmer switches
Understanding 3-Way Dimmer Switch Compatibility – When using two or more dimmer switches they must be compatible with each other. Some brands will require you to have Master and Slave units, such as Lutron.
Is it possible to have two three way dimmer switches? How to Make Two 3-Way Dimmer Switches Work Together.
Installing a Dimmer Switch: How to Install and Wire Dimmer Switches for Your Light Fixtures.