I am very confused, too, and the main problem is that the women look alike.
The woman in bed with the father looked very much like his wife (who presumably is the mother of Alice), and it was difficult to tell the younger wife from the older wife, except, I think, that the older wife, when Alice was dead, had a short bob.
Or was the older wife actually the woman who was in bed with the father? If so, why would Alice call her "Mum"?
Does the actual mother really think Alice is dead? Maybe the son, "Midget", knows the truth, and that is why he told the gravestone that he had not forgotten his promise?
And who was the woman who ran away from Midget when he was with his friends in the supermarket car park?
I am going to have to read the book superquick before the next episode to try and make sense of it all because it is just too troubling.