I would like to know whether it is possible or not to get rooms in CERN's hostels for my friends?

Unfortunately outside visitors cannot stay at the hostel. The rooms are exclusively for people working at CERN. However the hostel will be able to give you some addresses for hotels in the CERN/ Geneva area.There are also many hostels in Geneva centre, some of which have rooms / dormitories where one can stay for a few nights.