From the date you're adjusted to permanent resident, it will take about 7 years for your mom to become a permanent resident. Then, she can sponsor your brother as her son (he'd have to remain unmarried, I'm assuming he'll be over 21 but correct me ... he has to stay unmarried until your mom is a citizen which will be in about 13 years from when you become a permanent resident) and according to the current wait times it will take another 10 years or so for him to become a permanent resident through your mom's petition.
So total wait for your mom will be about 7 years and about 17 years for your brother, from the time you become a permanent resident.
4th preference (sibling) petitions for India have about 12 year wait currently, so if you sponsor your brother once you become a citizen it will take about 18 years from when you adjust to permanent resident. So your brother is looking at 17-18 years either way and the earliest you or your mom can file a petition for him is 6-7 years after you become a permanent resident (which is important because he may have a hard time to enter on a nonimmigrant visa after that).
These times assume that the wait doesn't significantly change (which is possible).
At the time when you become a citizen, if you find in the visa bulletin that it will still take about the same time if you sponsor your brother or your mom sponsors him after she becomes a permanent resident, it might make more sense for you to sponsor him, because he'd have to remain unmarried for your then-permanent resident mom to sponsor him until she is a citizen. If you petition for him, it's ok if he's married and this way his future family can immigrate with him as well, as his derivatives.
But, my recommendation is that your brother ought to look at employment based immigration anyway! Or hook him up with a US citizen lady!
