IMHO that's perfectly acceptable as long as all three of you travel together and you get three validation stamps before entering the tram or the train.

What Mark said - the key part being that you'd need to validate you ticket before you start the trip (ie, validate it three times before you get on for the first trip, then three more times before you start the return).
Oh, and machine validation - not just writing the details in by yourself.

Hello,

I faced a similar problem today!! I didn't know I am supposed to have a night ticket along with the normal train ticket. I have to pay CHF 75 as a fine for having not paid the 5.00 CHF worth night train ticket (damn unfair!!).

I cannot complain though. I cannot change the rule book of SBB, best solution is to improve my German and to keep my eyes-ears open for such rules that are not displayed/announced anywhere in the train station.

My only concern is :

Would it have an impact on my immigration records / work permit?

People who have come across similar problem, do shed a light

Thanks!!

No.

Would a holder of a GA (first or second class) also have to pay a surcharge for the night train?

I also didn't know about this surcharge until recently.

Yes

Jede Person braucht für die Benutzung des Nachtnetzes einen Nachtzuschlag zu ihrem gültigen Billett. Auch Generalabonnement Kunden brauchen den Nachtzuschlag. Ansonsten gelten Sie als Reisende mit teilgültigem Fahrausweis und werden gebüsst.

I've been living a life of crime.

Must be something local, I actually am almost amazed how one could miss this, stickers, pamphlets, it says on every timetable of the busses/trains on every station etc..

It is actually posted - also in english - at any train station