We are looking for a site where we can upload photo's, add our friends, and they can view and order prints without me having to invite them every time.
Sites which require you to send out invitations are a pain in the bum! You simply require a site which allows you to choose between making your galleries public (for anyone to view) or password-protected (so that you can provide friends with the password and they'll always be able to access the site without requiring an invitation). Fotopic offers everything you require: http://www.fotopic.net/
I can thoroughly recommend the kodak easy share gallery. I put all my pics there to view and for safe keeping in case of a computer crash.http://www.kodakgallery.co.uk