Unfortunately, you have made several serious mistakes. I wish you had come here before filing :
1. Your mother can have no derivatives. She is an immediate relative of a US citizen. You need to file a separate I-130 for your brother.
2. Your brother cannot adjust status through you as his priority date will not be current for more than 10 years in the future....maybe 20 years.
3. Your mother, as a legal resident, can file an I-130 for your brother, but it will be several years, minimum, before his priority date is current.
Do not allow your brother to file another I-485 now. It will be denied also. If his I-94 has expired, he is out of status.
I suggest you find someone who is knowledgeable of the process or an immigration attorney to help.