head on , i understand your frustration, even your parents are retired, you can still show the savings and tell them they are retired and if they have provident fund, pension etc . .you can show that too. they know many nepali do not have $ 40,000 in saving account ..what i would advise is tell your brother to attend the visa session organized by US embassy and asked few questions to the couselor, mostly those who come on orientation program are the couselors who takes the interview..

 if the guy is genuine student and genuine intention to study in a decent university  , who has decent academic credentials are very likely to get visa, financial documents are not something that they would look first..this is what they told when myself attended one of those seesions organized by embassy. 

tell your bro to do all the homework to gain confidence..and tell him to be genuine!!