I have 2 accounts on my ps4. One for me and one for my brother. If I buy a 20$ PSN gift card, will I be able to put 10$ in my psn account balance and another 10$ in my brother's account?
When adding a gift card to PSN you simply input the 12 digit code and all of the funds are added to that account. There is no way to split up the value to multiple accounts. This is the same for adding months of Playstation Plus to an account.