I did try to do this but as it is now I think we have to complete an order to register..I could only see a "log in" option, no "register" so perhaps he'll need to change this first?
Registration is on the checkout page. You hit a checkmark and create a password.
Yeah but if you do it the other way around, and make the shop and checkout cart part of the "members" section. Then that would almost certainly stop the shared cart problem.