It is a very subjective matter. It is not illegal to change the status from F1 to whatever else it is as long as their immigration laws allow. Yet I cannot understand the way the visa rejections take place. Of course there are cases where the kids dont even know what they are doing and blindly follow some education consultant's advice after paying a hefty sum to those blood suckers and I am sure that it's that kind of culture which puts the rest of the mass in the same level of scrutiny. A lot of kids even tend to shy away from taking toefl, sat or gre. They would rather resort to some blood sucker agent's advice as if they do not have their own back bone, who makes it look like migrating to USA is the solution of all the problems in life.

I guess all I can say is that be straight with the interviewer. Make it a case to let them know that you need to come back since your brother is a US citizen now (and that he has not broken any laws by taking up the new status) and that someone needs to be back in Nepal to take care of your parents and that you have other plans after your school is over.