Let me share a wise guess. Consular at all US embassies around the world watch all non-immigrant applicants as "Possible immigrants" and the most important thing is to make them change their view point that you are not an intending immigrant (since you are applying for F1 Visa). Honesty is the best policy but doesn't always help you to achieve what you want and what you deserve. You may have 1580 in GRE and 290 in CBT TOEFL with distinction in your studies, if you give them a slightest hint that you could be a possible immigrant then you are not qualified for non-immigrant visa. This is what law and policy say. Though Visa interview and KTM is more like picking bingo ping-pong balls, but in my opinion giving them info regarding your parents' PR and brother being here is a BAD idea. That way you won't have any STRONG FAMILY TIES in Nepal. Think over it and do what your MIND says (not heart).