Sharing my iPhoto Library with multiple users

Easy...

In Leopard with iLife '08...

Quit iPhoto. Back-up existing Libraries and then select the one account to be the main Library you will merge the rest into. Copy all of the photos from the other account into this one to make it the "master".
Copy that new merged library to the /Users/Shared/ directory.
In the Finder select the iPhoto Library in the Shared directory and choose Get Info... In the Sharing & Permissions section click the lock and enter the admin username and passsword to allow you to change the permissions. Change the permissions for "Everyone" to Read & Write. If there is Wheel group also change those permissions to Read and Write. Close the get info Window.
Re-launch iPhoto holding down the option key. You will get a dialog to create a new library or select an existing one. Choose select existing one and navigate and select the new master library in the Shared directory.
iPhoto will open connect to the new shared Library. Now quit iPhoto and repeat the steps for launching iPhoto while holding sdown the option key and selecting the shared Library for each user account.
Now all accounts should see the same library and be able to add, edit, and manage photos from it.
I think you could also place the shared Library on an external drive if you choose Get Info on the drive and tell it to ignore permissions.

 

Sharing

In iPhoto go to Preferences-->Sharing and set the option "share my photos". And your parents need to set the option "look for shared photos" in their iPhoto.

Works fine for me over the network. Haven't tested it on the same Mac though.