Ah, just to add. If your son bought digital DLC for Spiderman (physical disc) from the psn store then you should be able to share it.
You would need to do gamesharing (set primary ps4), and on your sons account go to his game library, navigate to spiderman and it's dlc. It'll show a list of available DLC and if it hasn't already automatically downloaded there should be a small button of the left of each entry that has been purchased. If you download and install them, then switch to your account you should be able to get all the DLC goodies as well.