ILR for child who was born in the caribbean

[Markenzie10]

I am 24 years old and i am a British Citizen by nationalization. I resides in the UK from 2011 til present. I am seeking some advise for my 6 year old biological son.
My son is originally from the Commonwealth of Dominica same as me but not yet a British Citizen, he traveled over from the Commonwealth of Dominica on the 31st of December 2017 on a 6 month visit(no visa) hoping to settle and live with my wife(step-mum),daughter(biological sister) and I(all British citizens). I am really confused as to what route he needs to take to settle here with us.visa/ILR/can i register him as a British Citizen?
I have a letter signed from the courts in Dominica from his biological mother(my ex) passing full parental responsibility and full custody rights over to me and hes Dominican birth certificate.

[vinny]

I think that child may switch to SET(F).

However, explain the change in circumstances since his arrival in the UK, as one condition for a visitor is that he leave the UK after his visit.

ILR is expected prior to Registration, but it may be possible without it.