Those two goals are mutually exclusive unless you set the ftp up to be anonymous ftp areas, or you include the password in the url (which I have never thought was a good idea from the browser).
By setting them up as individual ftp users, you have given them a safeish way to upload files, but not a convenient way for them to view those files from the web. ftp and http are two completely different protocols and serve two completely different purposes.
Your issue is a variation of one that has been repeatedly discussed on these forums: how to share files/webspace between/amongst users. There are many ways to do this.
If you want to do it the way you are proposing, the url will have to contain the individual password, which is a *bad thing" if you ever intend to have any of these urls publicly viewable from the web. If you are only going to send them the urls in an email. the risk is less .
What it sounds like you are really trying to do is to set up a collaborative workspace, and there are many scripts on the web, that run well at Dreamhost, to enable you to do this.