Not necessarily. There were comings and goings all evening and some uncertainty over timings and who was where and when.
Family and friends are not suspects.
I analysed them long ago and I no longer want to go into that area.. My own conclusions were; they were there too short to know the area that well to perform a perfect crime. Like me, I was in Vienna for 6 days and I have no clue about life in Vienna and don't speak German, and don't know anyone there.. so it would be pretty hard for me to perform a perfect crime in Vienna even if I had plenty of time.. and they were squeezed with time.. Could they have helpers in their friends, no. Not a single professional in the UK and I know many of them in my opinion would hide someone's crime and jeopardise their own life.. What for?
The second thing, they could not just get rid of their daughter and go and happily laugh and drink.. these people are people like us.. could you do it? And what for?
My own analysis plus the police saying they are not suspects summarises it well for me.. They are not suspects!