Since you have access of a ftp server (1&1 host). You can create a web/ftp folder on your PC. Click "My Computer", Click menu item "Tools" select "Map Network Driver". Then click example, it will show you how to do it. 3 of you just do the same thing, you can have the same web/ftp folder on your PCs.
Please check security arrangement, make sure only 3 of you can access the ftp account.