I tried to google it, but i found opposite answers... 1) Do i need a credit card to redeem the 3 months subscription code from some e-shop to the ps store? 2) If i'll make for my brother a second profile, will he be able to play online as well as i on my profile? Thanks

If you have a code for a subscription, you shouldn't need a credit card. I know 12 months works that way, but not sure about 3. Don't see why it would be different, though.

I'm pretty sure that as long as your plus account is the primary account assigned to your console, any other accounts on that system should be able to play online.

You can buy PlayStation Plus and PlayStation store gift cards from places like Amazon. It's been years since I really spent anytime there, but I'm sure places like GameStop and Best Buy probably stock them as well. So no you don't need a credit card.

There is a notion of primary accounts on systems. For example, let's say you buy Hatsune Miku: Project Diva Future Tone (as one does), your brother can create a new user, sign in, and play Hatsune Miku because both users are on that PS4. Some of that primary PS4 capabilities may or may not apply. I'm not 100% sure.

PayPal works too.

At some point, GameStop started just printing codes on receipts, eliminating the need for the actual cards to be stocked in store,. The last time I did it wa a few years ago- No credit card was required for the 12 months subscription, I assume 3 would be the same.

So long as the Primary account on the PS4 has the PS Plus subscription, all accounts should be able to do access almost all of the online functionality, with the exception of PS Plus discounts, automatic patch updating, and early beta/alpha access demos)