Flickr everyone can see, unless you make the photos private. What I would suggest is they all create their own acct, upload pictures and you create a group "Terry's Wedding" or what have you so everyone can send pictures to it.
Photobucket you can restrict with a password, but I am not sure if they can DL the full res if you upload the picture though
Those are about the only two I have dealt with. I love Flickr, and if you don't mind the pictures being public I think it'd be the most grandparent friendly and everyone else.