When your father had died your mother should have assumed the priority date of the petition and requested humanitarian reinstatement. However since your mother had already filed a petition and your brother was still under 21 when it was approved the. CSPA applies. However consulates around the world are notorious for denying beneficiaries even if CSPA applies in their case and after denial it falls into a rabbit hole that is so deep it requires a lot of work to get the case out of it and back on track. Therefore I highly advise consulting with a qualified Immigration attorney in order to get the job done right the first time around. This will not only being your brother here a lot sooner but will save you a large amount of money in attorney fees in the long run. Best of luck.
This depends on the immigration status of your parents.
(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.
From the facts you lay out it sounds as if the Child Status Protection applies. Best to check with an immigration attorney in person.
This advice does not form an attorney-client relationship and is merely informative. It should not by itself be relied upon to address a legal concern.