Combine both libraries into one and just add tags to the books (e.g. family, adult). The calibre content server already includes its own web server so no need for apache. If you plan on using the calibre content server, you'll need to use a separate port for each user with the necessary username/password and access restrictions.
e.g.
Code:
calibre-server -p 8080 --password "dad" --username "dad"
calibre-server -p 8081 --password "mom" --username "mom"
calibre-server -p 8082 --password "kids" --username "kids" --restriction "family"
However, the above would give you a different URL for each one.
If you want something more robust, the only way I could think of is for you to write your own scripts (in asp, php, python, etc) which would use calibre's metadata.db similar to chaley's Calibre PHP Server.
There's work being done on making calibre support a multi-user environment but I wouldn't expect to see a release anytime soon.