It depends. If they live in Switzerland, then I would advice for the adults the purchase of save offers online, such as saver day passes or single saver point-to-point tickets (depends on the connections they will take and how they're going to travel).
For the children under 16 I would strongly advice Junior Cards or Day Passes for children.
A 16 years old person is no longer a child for the SBB and will be paying the normal adult price.
But if they don't live in Swiss and will be here just for vacations, the best option would be a Swiss Travel Family Card.
As you see, there is no way for me to give you a simple answer as you wished. There are different informations to be taken in to consideration.
For that, the community is not the best channel for your query.
Please call us, so we can better advice you. Our Contact Center is there for you 24h per day on the phone 0041 848 44 66 88 (0.08/Min.) or if you're calling from abroad and this phone doesn't work, please try 0041 51 225 78 00.
Best Wishes. EllenvS.