I think Peter had it correct. First go in an create a group, say 'developer'. Then go into 'user accounts' and give each of your friends an account and make them part of developer group. Then create your ibay, make the group 'developer', make ftp 'write=group, read=(which ever choice is applicable)', and public access should be 'Entire Internet (password required)'. Now, by using ftp, anyone in the 'developer' group has access to put files in your ibay. I do this from internal network and external to the network. I hope this was helpful.
Good luck,
Mike