License sharing is a console feature and not a Bungie or Destiny 1/2 feature, and as such, Bungie doesn't offer direct customer support for it. That being said, you can try opening Desitny 2's Manage Game and Add-on menu and download the DLC unlocks while logged into your son's account. This normally fixes the issue you're having. It should be noted that the standard license sharing mechanic still applies, so he can only access the content when either on the same console your account is logged in to, or on your home console (whether or not you're logged into it). If you have further issues concerning the license sharing, you'll need to contact Microsoft. Only the account that owns the content is guaranteed to have access to the licenses, so any sub/sharing accounts are secondary and thus using a license sharing feature.