Topic: Gamesharing help?

So I am game sharing with a family member, (2 ps4s.)
We set each other's account as primary, I can access his stuff and he can access mine and we play together. However, we have another account with a DLC that we would like to use. If he gets the 3rd account primary then he cannot access my purchased content meaning we won't be able to play other games. Does that mean only one of us can use it since it's a 3rd account?

yes, you are correct. you can only access digital stuff on your PS4 that is owned by the primary account (if it's not yours) and anything you have purchased. if your PS4 is not the primary of the 3rd account, then you would have to log in to PSN on your PS4 as that user to access its content - however, because one of the other two accounts is not the primary on your PS4, you won't have access to that content. not 100% sure about dlc though.. it would be somewhat unusual where a base game and its dlc are installed on the same PS4 but have been purchased with different user accounts.