well samhavi ji,
its highly unlikely they offer visa for siblings for graduation, well parents can get it vey ealy but otehr than parents its realy realy hard, in ur case when u have gc another brother applying to study n ur parents already ahve visa, it makes them feel ur brother have much chance of immigration purpose ( ur most family member are here).
to get business/tourist visa one should show strong tie with home country i.e he sud own his good business, his all family are well settle in home sountry or he has good job in home country ..in ur brother case, it dosenot seem so..so there is high risk.
give u one example
a guy from my home town graduated in 15..since his mother did not showe any interst in his graduation so his brother ( who is a nepherologist in bir hospital) applied for visa..he was a senior docotor in government hospital n earned good had proper documents to show that he will be back..but councler denied saying cant offer visa to siblings n she was not sure if the woctor will be back.
if ur brother is not planning to pursue higher education in us or has not plan to come backin us in future u can give a try but if he intends to come usa in other visa ask him not to apply koz one he is denied in tourist its really hard to get other visa koz it shows his intent to be immigrant..but of course visa has sumthing to do woth luck too