This is based on past experience not on this case.
Jett's wishes will be taken seriously and most certainly considered due to his age, but as he is not necessarily Gillick competent (this is based on mental capacity, so if Jett has been diagnosed with anything that could affect his cognitive ability), this would be considered. It's also based on age, maturity, and understanding of the issue he is being asked about. Gillick was originally passed to gauge the decision-making ability of a child to consent to medical treatment but is now used as a competency test to see if a young person has the appropriate understanding to make a decision.
My gut feeling is that his past trauma is clouding the water as far as 'additional needs' alluded to by our very own stinky pissy pants. This will complicate things and take time. He could very well display signs of additional needs, but children often do when exposed to traumatic events. Jett comes across as sensitive and less resilient than his sister. How very ironic that the trauma he has suffered has been at the hands of his mother and, more than likely SB too.
I'm sure parental alienation is happening regularly. Kipper has consistently demonstrated she is incapable of being positive about any of her exes. I don't think she has the intelligence, knowledge, or compassion to realise the type of harm she is more than likely causing. The evidence is publically available that she will bad mouth ex-partners at every opportunity, even in the presence of children, so imagine what's going on behind closed doors. I think this happens as her need to 'win' overrides everything else. Even the mental health of her own children.
If I was a social worker talking to J&B I would be looking for the prevalence of the word 'disgusting' That would be very telling. It is usually fairly easy to spot children who are coached, by their use of language.
I would make an educated guess that Kipper has really done a number on those kids that will take years of therapy to untangle. I also wouldn't be surprised if Jett sadly develops all kinds of issues later - disturbed sleep, OCD, self-harm, anxiety and depression, and even an eating disorder. This can be prevalent in disenfranchised young people who have also suffered trauma.
It's so sad and so unnecessary.