Dependents do not need to file separate I-130. If dependents were listed on I -130 when Person A filed petition then they are all set. Now since your case is already approved all you need to do is wait for visa number. When visa number is available for your case US EMBASSY in Nepal gonna contact Person B in Nepal. Then Person B has to fill form DS-230 Part 1 and 2 where they include all dependents.That means Person B must inlclude all dependents when they apply for immigrant visa application that is DS-230 part 1 and 2. Hope you got all information.