Hello DenisZ
You make reference to this promotion:
https://www.sbb.ch/en/campaign/day-pass-for-2.html
For example, can my wife buy the Gornergrat railway in Zermatt with reduced price?
To answer your question, the answer is NO.
Both of you have to purchase tickets for routes not fully covered by the GA or the Day Pass for 2, respectively. You can purchase the ticket at half fare, while your wife has to pay the full fare for such routes. In fact, it is the Swiss Half Fare Card that grants the discount, not the Day Pass.
The Day Pass for 2 the same validity applies as for the Saver Day Pass.
Kind regards,
Roland