Your two younger brothers will be taken before a Judge for a "detention" hearing who will decide to keep them detained until trial (15 Court days) or can release them home with a date to come back and/ put them on HSP (home detention with an electronic bracelet). they will be appointed a Lawyer each and then have the right to have a trial. If found guilty they could be sent to a group home (up to a year) or to a probation camp for 4,8 months or a year. They can also be sent home on probation. they definitely need lawyers.
Robbery is a felony that carries up to five years in state prison for an adult conviction -- even more if it was a home invasion, or committed on public transportation or at an ATM.
If your brothers were 16 or older at the time of the offense (or even as young as 14, if certain provisions are met), they could be tried as adults, and might be looking at time in the Division of Juvenile Justice (formerly known as the California Youth Authority).
If they are 16 or older, a juvenile court finding that they committed robbery will count as a prior strike under the Three Strikes law in any adult felony prosecution. They would also be ineligible to have their juvenile records sealed.