How will I bring my mom with my 19-year old brother in US?

You can file an immigrant visa for your mother, and one for your brother, but your mother is an immediate relative, and your brother is not. Your brother may be able to enter on a student visa, but wait times for a priority date to become current for him will be many many years - possibly a decade or more. Once your mother has status she may also petition for him, perhaps shortening the wait time by half.

You really cannot. You can petition for your mom but your sibling's petition will take about 10-12 years if you petition for him as he cannot come with your mom as a dependent since there are no derivative status possible with an immediate relative petition. Once your mom enters the US she can petition for him but it will be about 4-6 years wait. The best thing to do would be to see if your brother can qualify for a student visa to come study in the US.

Your brother cannot be a derivative relative of your mom's petition. You will have to petition for him as your brother. Your mom can also petition for him after she gets her green card.

These matters are difficult to navigate. You should speak with a immigration law attorney in your area. He or she should be able to advise. Move quickly, however, as you do not want to lose options that may be available to you and your family. Good luck!