What sort of permissions does the "admin" group have on your system? That doesn't sound like a group you want to have the "apache" user in.
I'd create a new group that is specifically used for this purpose (updating directories that are served up by Apache). You can name it something like "wwrite", and put the "apache" user and your sftp user in it.
Ownership and permissions on such a directory could be set with:
# chown root:wwrite directory_here
# chmod 2770 directory_here