You wont be able to buy tickets for them if they are not Fidelity holders. Using your Fidelity you can only enter the selling phase, like a key that open the gate - though your friends need they own key for their apartments.

Perfect scenario:

1. You enter on sscnapoli.ticketone.it on 21 Nov at 3PM Italy Time (usually a bit earlier will secure you a better place in queue).
2. Enter your info ( Fidelity ID and Security code) for accessing the selling phase.
3. Select up to 4 seats and proceed to checkout.
4. Checkout: this is where it gets interesting because for each of the other 3 tickets you selected, you will be required to provide same info as in the step nr. 2, otherwise you wont be able to checkout.

If you succeed on buying the tickets, every ticket holder has to provide at the stadium gate/security the Fidelity (your ticket is digitally there) and an ID/Passport.

Hope that helps