Legal Question in Family Law in Washington

He needs to file a petition to establish paternity of the child and get an order for a DNA test once the child is born, although if for any reason the mother requires an amniotic fluid be drawn, he can ask the court for an order to allow the fluid to be DNA tested as well, and that will allow paternity to be established ahead of birth.

If he can afford it, your cousin is advised to do this with the an attorney. It will no doubt save him a lot of time and aggravation, because trust me, there is already going to be enough without him making needless errors on his own. Best of luck.