If you are adamant that ftp is the only way to go with this, then you could setup a crontab in each individual member's account that chown's the upload directory contents to your admin user every so-often, thus giving you full rights.
I think what you're trying to accomplish would be easier to do using php or cgi upload scripts which are linked to each member's folder. For example, [color=#0000CC]member1[/color] logs in and goes to the upload page. Anything he uploads is placed in the ~/domain.com/team/[color=#0000CC]member1[/color]/ directory.
That's probably the best analogy I've read that clearly explains/justifies ownership within UNIX.
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