Swiss Rail Pass purchase

Buying it on arrival is the best option. You would only need it in advance if you were traveling by train to Switzerland from outside the country and needed it to go into effect as you crossed the border. If they send you an email with a pdf file, you can save it and print it again. But then I've never actually bought a Swiss Travel Pass on-line.

Also, can the pass be printed out more than once in case of printer failure if printed at home?

Out of caution, I will "print" (save) electronic documents as a pdf file then print a paper copy. It seems that many younger travelers skip the paper copy and are depending on displaying documents on their devices, but I'm old enough to want the comfort of paper with a electronic back-up.

And I think the free Swiss Family Card doesn’t work for grandparents. There is a different card for grandparents taking their grandchildren. At least that’s what I seem to remember.

Correct, the free Swiss Family Card for visitors only works for parents and legal guardians. They used to have a separate, buy-in-Switzerland version called a Grandparent Card, but as of this year, grandparents, aunties, and basically anyone can buy a Children's Co-Travel Card. This is also mentioned on our Swiss rail page.

I failed to say that the children and their father will be traveling from Paris to Basel by train where we will meet them. Which is the best way for him to purchase a Swiss Family Rail Pass?

So their father will be with them and you the whole time? Trying to figure out these logistics.

I don’t know exactly how the Family Pass works, but for 2 adults, we bought pases online and printed them out, feeling good we could reprint them from the confirmation email, if necessary.