The manual description of that option says:
The first existing path that optionally contains the marker file is then used as the destination.
So you can’t have two destinations. You would need to use a separate sync tool to copy files from one destination to the second. Maybe you can call this in a script with --run-script-after.
It is a known bug that will hopefully be fixed in the next version. A workaround is to open the backup to edit and use the advanced options at the end.
%RESULT% is the big output that you have in your screenshot. If you only want success/failed, use %PARSEDRESULT%. I don’t know if that will be translated.
Did you look at this solution, maybe it works better than the integrated mails:
The file names on the destination are supposed to be this way. You can change the prefix from duplicati to something else, but I would not suggest it. These files do not correspond to your source files. They contain parts of the files, and only duplicati knows how to put them back together. This is so that the same data does not need to appear multiple times.