guitarcenter said it well. i did exactly as outline by him. your brother in nepal needs to get hold of a lawyer (others can prepare it too but you get the idea) who in turn will prepare a document as per the nepali law for you to be able to transfer the power of attorney in the presence of the ambassador in DC. lot of cheats misused the option to do it in absentia (fake land dealings in nepal) so that convenience doesn't exist anymore. i had to fly to DC too.

make sure your brother provides notarized copies of lalapurja, nagarikta, his pictures in the document as required (2 copies i think - the lawyer will get this going though) and get some spare ones too just in case. call the embassy and ensure that the ambassador is around that day/possibly next day too. he had meetings with some us government office and i waited two days to get his signature. you can avoid that wait hopefully with some careful planning.

call the embassy guys. they are overworked but will answer questions. people just blame them as not prompt and so on, but after seeing their workload and the amount of help they offer to those who walk in, i have nothing but praise for the embassy staff. under the circumstances, they were super efficient for me as well as for about 50 other people who came in while i waited.

sometimes folks in nepal won't trust your power of attorney document from DC (unbelievable, isn't it? but it happens and be ready for that. there's a whole process to validate that too). and this is most likely to happen if you don't go to DC personally. if that happens you will have wasted lot of effort. so long story short go to DC. and enjoy the free museums and other historic places there.

good luck.