Thanks snowyb - called them again and got someone else. This time there were no problems putting the kids on Flex 125 Explore plan and the two adults on the Flex 500 Explore plan.
Just to add that when I rang up, I pointed out that there was no facility on website to buy different plans for different family members (and therefore get the 10%discount ) they applied the discount over the phone straight away! Might help a bit
