You and/or your brother should file if you have income and need to file.
If you are not dependents, and you don't need to file, you can register as "Non-filers" on the IRS site.
Your mother should register also.
Your mother should register (unless she filed in 2018 and received a refund direct deposit, then her stimulus will be paid through that bank account for her)
It does not sound like you nor your brother could be supplying more than half of your own support, if which case you would not be eligible for a stimulus check, but I do not know your entire situation.
Even if your mother filed and claimed you, she would not receive any additional amounts because of your ages. (If your brother was 17 before 12-31-2019)
Below is the link to register with the IRS:
IRS non-filer link
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