You start with the relative petition and consular process.
Your mother can be completed fairly soon, your brothers will have to await the availability of visa numbers.
Of course there are other considerations when it comes to step relationships.
It is advisable to contact an immigration lawyer to discuss your case if you are not familiar with the immigration process or otherwise have concerns.
You are welcome to use the link provided to contact me to discuss your case.
Retain counsel to handle the entire filing including the immediate relative petition and the corresponding consular processing. Depending on the age of your step brothers, you may have an issue that should be addressed immediately.