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.