How do we get tickets either for a tour or just a train ticket and go on our own?
It has been a few years since we went to Stein am Rhine but I think we took the train from the airport. It took about an hour and a half. You will get off the train in Germany and cross a bridge over the Rhine and walk into the town. You can definitely do this on your own. Perhaps Chris in Basel can give you more advice on the trains.
Just get on a train from the airport. There are 4 trains every hour, and it takes ~1h10.
Look up train times on the SBB website: https://www.sbb.ch/en/
Your starting station is Zürich Flughafen, the one at the airport. Destination Stein am Rhein (there are many Steins' in Switzerland, make sure you get the correct one).
Buy the ticket at the station. It will cost CHF 55.60 return, assuming you don't have any discount cards. That price gets you a one-day pass for the Zürich region ("Z-Pass OSTWIND-ZVV Day Pass All Zones")
You will get off the train in Germany and cross a bridge over the Rhine and walk into the town.
Susan, at that point, both sides of the Rhine are in Switzerland.