Hello STACEYJUL,
Thank you for asking us. First of all ο αδερφός has a plural of οι αδερφοί (οι αδερφός is grammatically incorrect).
This plural (οι αδερφοί) is strictly masculine.
There is another plural form though, and that is τα αδέρφια. Since this alternative form is neutral, it may refer to more than one males who happen to be brothers or to siblings in general (brothers and sisters together). In natural and everyday speech, two boys who are brothers would be referred to us αδέρφια (neutral). Αδερφοί sounds too formal, and is usually used in the press or in company names. For example the Warner Bros. In Greek "Bros." is also shortened from αδερφοί (Brothers) to "Αφοί" (Bros.) For example check this page:
http://www.ioannidis-bros.gr/Τhe non-shortened version can also exist:
http://el.wikipedia.org/wiki/%CE%91%CE% ... E%AD%CE%BD(Greek)
http://en.wikipedia.org/wiki/Coen_brothers(English)
I hope this clears up things a bit. Let me know if you still have any more questions.
Kind regards,
Stefania
Team GreekPod101.com