I cannot find a definitive answer for this anywhere. Swiss Family Passes say they give free travel to a child under 16 travelling with a "parent". Another website says "parent or legal guardian". I am going to Switzerland in April with my brother. Can I use a family pass to get him free travel if I get an Adult Travel Pass? He is 15, I am 23.
It's official. I've had an email from the Swiss Travel System:
Thank you for your email and your interest in Swiss Travel System.
Unfortunately, the Swiss Family Card is only valid for children travelling with their parents. Therefore, if you travel without your parents the card is not available.
In that case we recommend you to buy a Swiss Travel Pass for children for your brother (50% discounted to the normal/adults fare) and a Swiss Travel Pass Youth for you.
It is now possible to get a "Carte Enfant Accompagné" (accompanied (?) Child Card (?)) wich allows a designated adult to travel with children for a year at the cost of 30.- CHF. I got one for each of my step-siblings and the only thing I needed was their ID/Passport. N.B.: I'm Swiss as are my step-siblings and I'm holder of the "AG" (yearly or monthly public transport flatrate(?)) so it might not be a thing for tourists.