Hm, think I have got something wrong - the person in the bodybag was obviously dead; there appears to be another person in hospital (I was thinking they were one and the same). So.... the person in hospital can't be a member of the family, because the daughter showed no reaction when the police said there had been news; so maybe that is Mark (or could it be the woman from the NHS that was fired and was stalking George?).
The tablets were Viagra, Mary pinched them, as she was trying to sabotage Mark and Vivienne's holiday. I don't think Mary took the Viagra, as she was reading the leaflet that came with them. Still think Mary is the villain, but..... is that too obvious????