Photo sharing with offline viewing for the iPad
Dropbox would probably do this. Or at least some of this. 

It is possible to set up several Dropbox accounts (i.e., one for you and one for different family members) and share folders between those accounts. This would enable you to upload photos and they would be shared immediately in the shared folder. 

Dropbox provides a Photos folder which can be organised into a web album for viewing via the web page or in the iOS app. The most recent release of the iOS app has just included photo cacheing so that it doesn't need to be online to show photos. 

Not entirely sure that this would be a great solution but it might solve some of the issues. Also, not entirely sure that the sharing and photo features work quite as I have described but would be worth experimenting with.



This link explains how to set it up: http://www.makeuseof.com/tag/quickly-set-share-beautiful-photo-galleries-dropbox/