I did query ADHD with the school - via DP - and we had to do a questionnaire, as did his mum. It was decided he didn’t have it.
I do wonder if it’s symptomatic of ADHD.
OK.
The questionnaires have been completed and submitted and the professionals have decided, based on these, that he doesn't meet the threshold for further investigation into ADHD at this stage. That doesn't mean he definitely doesn't have it. But it does mean that it's not something that is going to be pursued at this stage unless you pay to go private, when they still might decide he doesn't meet the threshold for assessment.
What you do have though is a child who is living in less than ideal circumstances, whose life is chaotic for a 7 year old.
Before you pin your flag to the mast of ADHD and decide its that and nothing else, I would strongly recommend that you get real life professional advice and support for him and yourselves in terms of parenting a child who has experienced trauma.
There are certain traits of adhd and autism that are mimicked in trauma responses in children. A lot of parents feel more comfortable with the idea that their child is autistic or has adhd rather than trauma, for exanple, because the latter carries a sense of 'blame' or responsibility. And not all of those children will have been exposed to trauma so it's not likely to he an explanation anyway. But your stepson has and you feel yourself that he's a product of his environment.
What you have described in terms of the repetitive conversation could, for example, be an example of him trying to keep himself 'alive' in the conversation. To know that he is still 'there' and can be seen and recognised by other people. It's how he knows he exists. Because while you're talking to him, he can't be invisible.
To give you an example, my son was a similar age when his sister was born in quite traumatic circumstances. Within a few weeks, his grandad and his wife had a child who was very ill and had a number of significant disabilities. For about 6 - 12 months, my 7 year old son asked me in all seriousness if he was a ghost now or invisible because his parents both disappeared into hospital with his sister and then his grandad disappeared as he and his wife became understandably consumed with their own baby and putting things into place for her. This was despite his dad and I only being away from him a for a relatively short time and other family members being brilliant in their support. But he did effectively lose a grandad who had been very involved in his life up to that point.
You say his mum isn't supportive. In reality, the whole situation has been created by the decisions the adults around him have made. His parents split up, you and his dad were in a serious enough relationship for him to have a half sibling at 5, he's been living between two houses, there are parenting issues at home with the older siblings and his relationships and there is talk of isolating him further within the family (keeping him away from the toddler). I'm not saying this to blame anyone but there is responsibility on all parts for this situation and in terms of resolving it.
If you approached it with his mum in a way that meant she felt included and where the focus was on supporting the child rather than blame on the adults, do you think she is likely to be less defensive about her little boy being criticised? Would she be more likely to engage?
What have school noticed? What can his school offer in terms of pastoral support? Have his parents had a meeting with school so that everyone understands what is happening for this little boy? What have they said?