@Flossyrocks
I posted earlier about the needs of your existing children. But I’ve been thinking all day about this little boy. And honestly I think your DP is being selfish. He is acting emotionally and making this boy’s situation about himself and his history not the child’s needs.
It sounds like his DN has been abused and neglected for a long time, possibly all his life. His life is now being upended again. He is extremely vulnerable and now finally there is a chance that professionals will provide him with the much needed support and care he needs. This is his opportunity! He is only 10, still very young. There’s a chance that with the right support he will develop into a healthy happy teen and young man.
In a few years he will be at secondary school, nearly a teen. This is a much harder age to effectively intervene in a child’s life. If your DP gives it a go and fails, his DN will suffer much more than if he allowed the professionals to take the lead now.
And it seems highly likely your DP will fail.
His plan is nonsense.
Lying to SS.
Pulling the child out of education.
Giving him a sofa to sleep on.
Taking him to work every day rather than school.
Isolating him from his friends.
Chucking him into a chaotic blended family with a new baby and hoping he’ll cope.
Your DP is neither teacher nor psychologist.
Madness and cruel.
Hopefully the school safeguarding lead will not allow him to be off/rolled in this situation. Because it would not be in his best interests.
If your DP tries to execute this plan he is a risk of being assessed as an unsafe influence and being allowed no contact with the boy.
Much better for everyone if you and your DP allow the authorities to do their thing. Then once DN is settled and you are all settled, look at how you can be a loving uncle and aunt with visits, events, celebrations on an ongoing basis.