That is one very big hole he will be digging if he gets caught out.
just do everything you can do 100% legal then if you get some difficulties you can explore other avenues, but if you shoot yourself in the foot from the outset you will have nowhere to go.
Try to find the mother, but if you fail get a good family brief for sound advice, if you know or have a pic of the mothers ID card and the area she lives in the cops will find her for the cost of a brown envelope just go see the chief dick in the station.
Good luck hope you succeed