Does this have to be done under yast?

#> mkdir /home/ftp
#> useradd -d /home/ftp user1 -c "FTP User" -p mypassword
#> useradd -d /home/ftp user2 -c "FTP User" -p anotherpassword
#> chmod 766 /home/ftp

Of course only one of those users can actually "own" the directory.
As you said, this isn't a best practice.