Swiss Rail Pass?

Swiss trains are very, very costly per mile, so it's worth spending some time on this decision.

One possibility for your very long stay is the one-year Half-Fare Card. I know that's more time than you need, but the price is a comparatively reasonable CHF 185. However, the annual card auto-renews, so you'd have to remember to cancel it well before the renewal date.

I have never used any form of Swiss half-fare card myself, and I don't know that this is definitely the best solution for you or part of the best solution for you.

Kate,

You may already be aware of this but one point to mention. AFAIK, Switzerland is part of the Schengen area, so if travelling with a U.S. Passport you'll be limited to stays of 90 days in any 180 day period. The 90-day allotment includes your arrival and departure days. There can be fines and other penalties for those overstaying the limit, even for short periods.

Regarding the Swiss passes, you could have a look at the Half Fare Card, which is valid for 30 days - https://www.myswissalps.com/swisshalffarecard . Depending on how much travel you plan on doing, you could buy one each month. Perhaps your friends in Switzerland could recommend a solution?

I would also point out that if you are non-EU/Schengen citizens, you are limited to 90 days in any 180 in the Schengen Area, which does include Switzerland.

The Half Price Card has a tourist version, at CHF 120 for 1 month, or the residents version, at CHF 185 for one year. For the annual card you need a Swiss address (it is posted to you) and it renews automatically, you have to cancel it.

Once you have a Half Fare Card, you can convert it into a full pass valid one month for CHF 420.
See here (section "Supplementary offer: 1-month travelpass for the half fare travelcard"): https://www.sbb.ch/en/travelcards-and-tickets/railpasses/half-fare-travelcard.html

Most parts of Switzerland have regional passes for residents. The one I have covers the city plus surrounding areas, and costs CHF 80 per month or CHF 800 per year. This covers most of my daily needs.
There is a list of the regional fare networks here: https://www.sbb.ch/en/travelcards-and-tickets/fare-networks.html

You can also get an annual pass for the whole of Switzerland, CHF 3860 for the first person, CHF 2700 for 2nd person in household
Details: https://www.sbb.ch/en/travelcards-and-tickets/railpasses/ga/adults.html
These also need a Swiss address, and require cancelling if you do not wish to renew.

There is nothing designed for 3 month stays. There are tourist passes, for less than a month, and residents passes for longer periods.

The annual Half Fare Card is the way to go, and I guess if you are house sitting, you will have a Swiss address. But sort out the 90 day thing. Unless you can get a long stay visa, you will have to shorten that 3 month deal. Don't cut it too close, as the 90 days includes your arrival and departure day, and you don't want something like a last minute hiccup to put you over the limit. So plan on 84 days (12 weeks) and leave some cushion in there.

Thanks, everyone. Whatever we do, it's not going to be cheap, I see. (But then nothing is cheap in Switzerland!)
And thank you for - wisely - pointing out the 90-day limit. We plan to leave Switzerland a few times during our stay which should theoretically subtract days from our presence there. Will getting our passports stamped by the Swiss authorities each time we enter/exit suffice to prove that we're not overstaying?
All advice and suggestions appreciated!
KateN

Your journeys away should be outside of the Schengen zone, like to the UK or Ireland or Croatia. Yes the stamps are proof, but they keep electronic records as well.

We plan to leave Switzerland a few times during our stay which should theoretically subtract days from our presence there. Will getting our passports stamped by the Swiss authorities each time we enter/exit suffice to prove that we're not overstaying?

That will only work if you travel outside the Schengen Area, for example to Croatia or the UK.
The Grenzwache (Swiss Border Guard) will stamp your passport if you are entering or leaving the Schengen Area, but not if travelling within the Schengen Area. You will never get your passport stamped at the land border as all surrounding countries are also in the Schengen Area, you will only ever get it stamped at an airport.
And your arrival and departure days count as full days. It is only complete days outside the Schengen Area which will not count against your 90 days.

Whew! I'm glad I asked! We've no plans to leave Schengen, so it sounds like we've got to get busy on Plan B. Years ago, we had Swiss residence permits for several years while working there (1985-89).
Any idea if it's possible to renew these for this period, perhaps with an attestation from our friends? Or is there another visa we should apply for? We will be in the same canton (Fribourg), but of course, will not be employed in any way this time.

You will need to contact the Swiss Embassy in Washington or Consulate in New York. I would not get your hopes up. There usually needs to be a solid reason. And lets hope they don't consider an informal house sitting arrangement as "employment". Otherwise, plan on some vacations from the vacation to the Emerald Isle and the UK.

So let me get this straight. If we fly to London for a long weekend in the middle of our Swiss sojourn, when we fly back to Switzerland, the 90 day limit starts all over again?

Years ago, we had Swiss residence permits for several years while working there (1985-89). Any idea if it's possible to renew these for this period,

I doubt it. To get a residence permit for a non-EU/Schengen citizen you normally need an employer who can give evidence that they couldn't get a suitable employee who didn't need a permit. Your old permit may have been restricted to one employer, they often are.
It may be easier to get a residence permit without a work permit. Permits are handled initially by the cantonal authorities (Fribourg). I did a search for "Fribourg permis d'étranger" and came up with this page: http://www.fr.ch/spomi/fr/pub/etrangers_ce_aele/etrangers/les_autorisations_de_s_jour.htm
Or in German: http://www.fr.ch/spomi/de/pub/auslander_eu_efta/auslander_eu_efta/die_bewilligungsarten.htm

I also found these two: http://www.fr.ch/ww/fr/pub/faq/sejour.htm
and: http://www.fr.ch/ww/de/pub/faq/aufenthaltsbewilligung.htm

Wie eine Aufenthaltsbewilligung im Kanton Freiburg erlangen?
Drittstaaten
Wenn Sie Staatsbürger/in eines Landes sind, das nicht Mitglied der Europäischen Union (EU) oder der Europäischen Freihandelsassoziation (EFTA) ist und wenn Sie sich nicht auf das Freizügigkeitsabkommen (FZA) berufen können, müssen Sie im Besitz Ihres gültigen nationalen Passes und wenn nötig eines Visums (Schengen) sein, um in die Schweiz einzureisen. Sie müssen vorab ein Visumsgesuch bei der an Ihrem Wohnort zuständigen Schweizer Repräsentation einreichen. Dem Gesuch müssen verschiedene Dokumente beigelegt sein, je nach Zweck Ihres Aufenthalts (Arbeit, Studium, Aufenthalt ohne Berufstätigkeit).

"How do I get a residence permit for canton Fribourg?
If you are a citizen of a country which is not a member of the EU or EFTA, . . . . You must make a visa application beforehand to the responsible Swiss representative where you live".
Doesn't sound hopeful.

So let me get this straight. If we fly to London for a long weekend in the middle of our Swiss sojourn, when we fly back to Switzerland, the 90 day limit starts all over again?

No. You can by in the Schengen for 90 days out of 180 and they count the day you arrive and the day you leave. If you can fly to the UK for say a week, you can stay a few days longer. There are online Schengen travel calculators. Might be a good idea to play with one.

So let me get this straight. If we fly to London for a long weekend in the middle of our Swiss sojourn, when we fly back to Switzerland, the 90 day limit starts all over again?

NO!. It is 90 days in any 180. Which means when you return, if you have been in the Schengen Area anytime within the last 180 days, those days still count.
Or, put another way, if you fly to London the clock stops, and when you return to the Schengen Area it continues from where it left off.

Great info! Thanks for all the help. I appreciate it.
KateN

You should look at buying a Global Eurail pass before you leave the US that fits your travel needs, unless you are not planning on seeing any countries, but Switzerland.