I know it's quite common to think like that for poor students, trust me I was there also. All i can tell you is, it's not good to put too many people in a double room. Of coure you can try but i'm not sure if it's worth to take the risk that stuffs may force you to leave or even ask for fines. Maybe you can check hostel or book one double room and one triple room.
There is many other ways to save money like stay in pub overnight and sleep on the beach during the day. Or even sleep outside during the night, if your trip is placed during summer.
There is many other ways to save money like stay in pub overnight and sleep on the beach during the day. Or even sleep outside during the night, if your trip is placed during summer.