Hi Carole
You read it correct: the records of many Swiss Cantons are not (yet?) available online and research has to be done in the respective State Archive. The State Archives usually don't have time to do lookups, so you might need to reach out to a professional genealogist.
In Switzerland, the church books were the official records until 1875. From 1876, the civil registry records were / are the official records. For Canton Schwyz, the older civil registry records are also in the State Archive. Maybe their website helps a bit (you could use google translate):
https://www.sz.ch/staatskanzlei-departemente/bildungsdepartement/amt-fuer-kultur/staatsarchiv/besucherinformationen.html/72-416-387-380-2480-2531-4926-4932
Maybe FamilySearch has the microfilms digitised and they might be available in the Family History Centers. You would find this information on their website, if you search for records.
Yes, many of the same surnames at the same place as well as intermarriages are quite common (at least in Switzerland, partly probably in Germany and for sure also in Italy - I don't know about other places, but I'm sure there are more).
For Switzerland, we have the special thing called "Heimatort" (place of origin, sort of citizenship). The Heimatort is given by the father to their children and at marriage to his wife. The Heimatort remains, while place of birth, place of living etc. can be different. My family doesn't live at our Heimatort anymore for at least 100 years. But the Heimatort is official and usually also mentioned on records. So this helps to sort out different families with the same surname. Usually you can assume that people with the same surname and the same Heimatort are somehow related - but this might be back in 16th century or even earlier.
And of course there are chances that there are father and son or cousins with exactly the same names. So there is quite some work waiting to do. Sorry that there is no easy way :-).
