I doubt the familysearch records are 100% complete, I would not take a lack of a marriage for them in that set of records as a sign they didn't marry in Switzerland.
You should work on records in the US first:
-any later records (marriage, death, obituary) for the Albert that show where he was born or give the maiden name of his mother
-any later records for Susan (death, obituary) that might give maiden name, more exact place of birth, or parents' names.
-any records for William that can lead you back to his family in the UK - might be able to work out why he might have been in Switzerland and/or Germany.