Michigan law provides a special exception for individuals who have limited criminal convictions to have them expunged from their record under certain circumstances. Specifically, five or more years must have passed since your most recent conviction or imprisonment (whichever is later) and you cannot have more than one conviction expunged from your record. I'm sorry to be the bearer of bad news, but based upon my interpretation of your facts, removing your six convictions from your criminal record is an unlikely outcome.
No. Convictions don't "come off" your record. You would have to move to have the conviction set aside (expunged). However, since you have six convictions, you are not eligible to have ANY of them set aside (expunged). The one that your brother had probably never made it to his record in the first place. If fingerprints and paperwork are not handled correctly by the prosecutor and court, the Michigan State Police records division will not be able to create a criminal record file. Thirteen years ago, some jails and courts were still using ink to print people and this caused record keeping problems as the prints had to be mailed. Now, all jails and courts use "livescan", which is an electronic scanner of the prints. The scan is then sent electronically to the MSP records division. In addition, some driving misdemeanors and local ordinance violations are not required to be abstracted to the criminal record and under uncertain circumstances will even "fall off" the master driving record. With these, some courts abstract them and others do not.
No, they do not automatically come off your record. And, as stated above, you are only eligible for expungement if you have had only one conviction.