This reads like a classic work of nursery fiction which reinforces the stereotype of wicked stepmums 
The new wife has been married to the DCs dad for 9 years, over twice as long as the DCs parents were married. Hardly new, is she; unless the status of first wife is somehow elevated compared with all subsequent spouses?
It repeatedly refers to custody which is a US term, not UK - do the DM not know this, or are they using that particular term because it is more emotive than residency?
As for the quotes from the adults involved, they don't flow, they are disjointed and I'd be prepared to speculate have been taken out of context.