NanaandGrampy,
It is the continual messages of inconsistency from the parents (disagreements) which will not 'allow them to fix it'.
shysal,
We recommended they watch Mandy Saligari on Channel 5. They watched the first programme and then decided not to watch any more as "we see enough of that sort of behaviour at home without watching more of it."
obieone,
Our son has tried to change things but wife's lack of consistency in the decision making and discipline issue process makes constructive dialogue almost impossible.
As a last resort the only thing we could think of which 'might sink home' and make them think hard about their destructive behaviour towards the child is a book which outlines inconsistent parenting and the ultimate possibility of professional involvement.