Two-way mode with TX Ultimate

Is it possible to install 2 TX Ultimate using a Two-way configuration? For example the tipical stairway setup… control the same light from both beginning and end of the stairway

Since you are using a smart switch, you can add a wireless one on the other side of your stairway and set scenes to sync them.

But TX ultimate might not work, you need R5W.

Yes, it is possible. However, this is not a useful application. It depends on the wiring of the lighting system. In general, TC Ultimate does not support multiway switching. Turning a light on or off from either end of a flight of stairs requires two SPDT switches.
In theory, a much better solution for the traveler system would be to use two S-Mates and, for example, a MINIR switch. Either for a new switching system or to replace an existing one, in any configuration. What’s more, with an S-Mate you can extend such a system with several more switches.
Tell us more about wiring existing in your place.

Yes its possible. You would just have 1 switch that is physically connected to the bulb.

The other switch can be installed using just live and neutral wires. Ignore the rest.

Then setup automations
Turn on downstairs light switch also turns on upstairs light switch.

Turn on upstairs light switch turns on the downstairs light switch

And 2 more for turning off.

This way both switches will be kept in sync and can be used to turn on off the bulb thats connected to only 1 of the switches.

You can do this with scenes:

Create 4 scenes
Scene 1 :
If TX Ultimate 1 channel 1 ON
then make TX Ultimate 2 channel 1 also ON

Scene 2 :
If TX Ultimate 1 channel 1 OFF
then make TX Ultimate 2 channel 1 also OFF

Scene 3 :
If TX Ultimate 2 channel 1 ON
then make TX Ultimate1 channel 1 also ON

Scene 4 :
If TX Ultimate 2 channel 1 OFF
then make TX Ultimate 1 channel 1 also OFF

In this scenario it does not matter which TX ultimate phsycially controls the light, because both trigger the other one so both will control the light