You need to do some basic searching and find some caresheets. There are tons of information regarding leopard geckos.
Being raised together will not stop them from breeding. They're animals. They'll go at it regardless.
Breeding season, usually starts around end of December or January. Just placing them in with each other should be successful.
For more info there's tons on the web and I'll provide my caresheet link below.
http://www.reptilekings.com/caresheet.htm
Best of luck,
-Sam