Have Digital Ownership but cannot download the actual Game?

No. Digital games cannot transfer ownership and signing into someone else's account is a violation of the code of conduct. So you would not be the actual owner of the games and you would be putting yourself at risk for being banned.

Unfortunately you would have to purchase the game for yourself. Digital content cannot change ownership.

The only way you would be able to do so is to buy it. You basically only have access to the game because the original owner left the console as their Home console, but you don't actually own it. Digital content cannot transfer ownership.

It's best not to advertise it. If you sell it, it would actually be best to factory reset it and change it so it is no longer his Home. Digital content ownership cannot be transferred or sold to anyone else.

You can't. Digital ownership cannot be transferred.