You're right and you're wrong.
I know a lot about PS4 game sharing now (2 of my friends may or may not be currently game sharing with me on PS4), so I can give you an informed answer:
Whichever PS4 is the "primary system" for a PSN account, every user on that PS4 gets access to the digital content that the user has purchased, such as PS+ and games/DLC. That's why your brother can play online multiplayer even if he didn't buy PS+; you bought PS+ on your own PSN.
However, if you are logging into your PSN on a PS4 that's not registered as your primary (such as a friend's PS4), you can still access your digital content, but only that user can access the content. This is a precaution by Sony to avoid game sharing; that's why the PS3 method no longer works anymore. On PS3 you would just log into your PSN and download your content onto that PS3. You can still do that on PS4, but the content will be locked to other users since that PS4 is not your primary for that PSN (remember, primary PS4s let all users access the content of the primary user).
However, this is where the loop-hole comes into play. If you make your friend's PS4 the primary console for your PSN account, every user on his PS4 can access your content - including his own PSN.
Once your friend's PS4 is the primary console for your PSN account, your PSN account on your own PS4 will be a "secondary" account. In order to use your content, you must always be signed into PSN. If you aren't, the apps will be suspended for ~30 mins until it detects connection again. Also, if you have any other users on your PS4 such as siblings, they won't be able to access your content. Additionally, I'm not 100% sure about this, but I think if you want to buy new digital content, you need to do so via the primary console. This means buying content from your friend's PS4, or temporarily making your PS4 the primary to make the purchase.
Sorry for the long post, I wanted to be as concise as possible so you understand how it works.
TL;DR: To gameshare on PS4, make your friend's PS4 the primary system for your PSN account and vice versa. You guys have total freedom, with the exception that you must be connected to the PSN to access your content, otherwise it'll get temporarily suspended. Also, other users on your PS4 won't be able to access your digital content. Lastly, I'm pretty sure you need to purchase digital content from your friend's PS4 (since it's primary) for the content to go to both of you.
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