I would suggest that you speak to a lawyer becuase the process is a lengthy one, but these are the main points that you need to know when talking to a lawyer:
According to the rules, as a citizen, you can sponor your brother but the problem is that his green card is probably not going to come up for another 10 years! If your brother is married, you can include his wife and kids in the same petition but you would need to show enough income to cover yourself/your family as well as your brother and his family.
The legal implications of bringing your brother here as a sponsor is that you are legally responsible for him and his family for 5 years after he comes here. So if he or a member of his family goes on state supported programs like Food Stamps within five years of arrival, the Department of Social Services has the ability to come after you to get that money paid off...(just so you know. Many Nepalese sponsor people that they know --or don't know and often get into messy legal situations becuase of it)
The immigration system has categories (four in all) and a U.S citizen sponsoring a sibling either married or unmarried is the one that has the least preference therefore, it is category 4. The wait time depends on how many petitions they have from Nepal and what year the BCIS - Bureau of Immigration and Citizenship is currently working on (As far as I know, the current year for Preference 4 is still the late 1980's)
As far as the lawyer is concerned, like I said, I would advise you to get a lawyer because you have to file an affidavit of support and that would require you to calculate all your assets etc; however, BE CAREFUL IN CHOOSING A LAWYER because some of them will ask for anywhere between $2 - 4,000 for this petition and may not do a good job with the paperwork. One way of avoiding getting ripped off is calling the Bar Association of the State and getting a referral from them..most Bars have lists that they maintain and should be able to provide a referral fairly easily.
Good Luck!