I should have posted this sooner for those who were interested, but I'll tell you now what happened to the Harry Potter Dilemma.
The afternoon of the day it had happened I called the girl and asked had she bought copies for her children to keep, because she may have mixed them up. She realised her mistake and said we would swap them back the following Sunday. However she was dropping her daughters off at the pantomime we took the GB to on Friday night and had brought the DVDs with her to give to me and told me to keep the other 2 that she had given me in case the originals were damaged seeing as they had been on loop for weeks and weeks.
Regarding the other "dilemma" of whether to buy order of the phoenix or not, I've decided to wait for several reasons, mainly cos of lack of funds though lol.