No, if you try to log into the same PSN account on a different PS4 while online, it will kick the other login off. You will both need your own copies of the game.
If you play on your own accounts, it should be fine. The PS4 should simply check that you are allowed to play the game, which by your brother making your console his primary, it should.
On the bottom of the keyboard, there should be a button that looks like it has three dots. Please select that, and then select "select all" or "select text". After then you can click on the three dots, and then hit "Copy".
After that you can paste the same text via that same menu to another text box.
You are warned about the temperature at 85-90 degrees Fahrenheit, or around 29.4-32.2 Degrees Celsius.
The console starts shutting down when it reaches temperatures of over 95 degrees Fahrenheit, or around 35 Celsius.
This is to prevent permanent damage to the solder and wiring inside of the PS4 itself. If the thermals are bad and they need fixing, they ...