I use TrueCrypt to create a container and then I put sensitive files in that container. When the container is closed or "unmounted" it becomes encrypted. You can use TrueCrypt to mount the container and thus decrypt the files. All your family members would have to know the password. You can share the container anyway you wish. I like Dropbox because it uploads any changes made inside the container automatically when you unmount. I like TrueCrypt because its free and can be installed on any operating system.