Yes, the interviews were held before the exams and after the interview my DD mentioned they asked her about what is CURRENT i.e what is happening around the world and UK. At that time my DD mentioned about financial crisis in Greece and Middle East situation. My DH prepared her for that thinking they would ask these questions.
Also they asked her about her activities she gets involved in and what are her most favourite and least favourite subjects at school.
They also asked her what her parents do....(I suppose to see if we are able to pay the fee if she is offered a place
About passing both Wally Girls and Nonsuch; after visiting the schools you will clearly have a favourite. We did - Nonsuch. So we put Nonsuch as number one choice and then Wallington as our second choice. Best thing is to put the school you like best as the first choice if you have the right marks for it. If Nonsuch did not offer us a place then our second choice would have been our first choice. i.e if my DD did not get Nonsuch then she would have been offered wallington.
So give you a short answer you would need to put both down according to your pecking order.