Question for Ethiopian Airlines

Hallo,Am from the Netherlands and i want to book a ticket from frankerfurt Germany to mombasa.Ihave a brother who lives in kenya.Is it possible that he buys the ticket from thre for me,because in Netherlands they dont have an office i have only to buy via online and i dont have mastercard.How much is the ticket for 2adult and two children of 3 en 8 yrs?