You can certainly book two rooms and as long as his name was on the guest list there wouldn't be a problem. I see no real reason why he couldn't book it himself but would suggest it may be easier for you to book both rooms from the UK as that way you would both be sure you had confirmation of the booking before arrival. Although not guaranteed, this may also lead to both rooms being close to one another, or at least on the same floor. He would need to show his ID card at reception, the same as you show your passport, but being Tunisian I'm sure he would be aware of this.