help with new chicks

Hi, i hope some one can help me, i hatched out 5 chicks, and 3 died with in mins of each other, not sure why, but that left 2 chicks on their own, the question i want to ask would they be ok, on their own or should i get a couple more to keep them company or can i put them with the older chicks when they are old enough to go out side, they are 3 weeks old than the new chicks, thankyou if you can help