My question is the following: If i create a second account in my brother's ps4 console, then i will be able to play all the games that he's got in his own account! But what happens when i want to buy a new ps4 console of mine? Will i be able to play all those games that i enjoyed in my brother's ps4 console or am i supposed to buy all of them in order to continue from where i was? Thanks in advance!!! :) :)
I've answered this same question here: https://gaming.stackexchange.com/a/271692/51332
Short Answer is that as long as you don't have a "Primary" PS4 attached to your account, getting the second one in the future will not affect you. You can play on the current PS4 as a sub account and upgrade in the future without losing anything (like trophies data). On the other hand, he can attach his account on your PS4 to share his library with you. (You'll need to redownload the games of course).
Now in regards with just having one account to share, that's possible too. From the same page:
On how many SEN accounts can one device be activated?
You can activate a PlayStation system on as many SEN accounts as the highest number of possible local user accounts on the system.
This means that you can activate a PlayStation 4 or PlayStation 3 on up to 16 SEN accounts at once and you can activate a PS Vita, PSP or PS TV on one account at any one time.
There's a link on the page as well to explain how to share your account's content with your "friend's" console:
Create a new Local User account on the PlayStation 4 and go to [Settings] > [PlayStation Network] > [Sign in]. Note that system parental control settings may restrict this option.
Sign-in to your SEN account.
Select ‘No’ when you are asked if you want to activate this PlayStation system as your ‘Primary PS4’. This is to ensure you are able to continue to access your PlayStation Network content on your own PlayStation 4.
You and your friend now have temporary access to your PlayStation Network content from your friend’s system.
Using these steps, you can make the first account, tie it to the first PS4 and buy the majority of games onto it. Make the second account, tie it to the second PS4, log-in and save the first account's credentials to the second PS4 as well to share those games between the two systems.