As I have said, it is a huge red flag in the different ways he behaves when he is aware he is being filmed to when he is unaware.
The big smiles are so forced and unnatural looking when you see the candid moments sand realise how he actually looks at her and speaks to her when he thinks noone can see.
Sarah can try to put out her false narrative of them as the perfect family unit but the tension between them is do obvious and they are both eating and drinking to excess to try to convince themselves all is OK.
Poor Luke stuck in the middle of this, cue the question box full of statements of how happy they are when it is obvious to a blind man that they are not getting along!