Jan 13, 2011 - 2:39 PM
Yes, a Swiss Card would be best for all of you, assuming you will all be doing the same trips. An additional pass will not be necessary from what I can see from your description. You will only make short trips to and from your hiking area, and the Swiss Card provides a 50% discount on that. Buying more passes would not be economical.
The Swiss Card covers any train within Switzerland, except the seat/sleeper reservations for those trains that require pre-booking (such as night trains and most other international trains). The map we link to from the Swiss Card page shows exactly where its validity ends. From that point on, you need a ticket or pass for the Italian portion of the trip.
You can travel to Venice overnight, but day travelling would be faster. In one day, you can travel from Lauterbrunnen to Venice and even make a stop for a few hours on the way, e.g. in Milan or Lugano. But you can best check the timetable
to see what's possible.