Parent petitions are immediate relative categories. They cannot have derivatives, so your brother cannot be listed to join either of them. This means that you would have to put in a separate petition for your brother as a sibling. There is no distinction made for age, etc for sibling visas so that would be 15-20 years before he can get a visa. Clearly this is not workable for your situation. What most people do for this type of situation is petition the parents, then once they have green cards one of them petitions their minor child (approx 2 years process, maybe longer now) and then one or both parents gets a re-entry permit to allow them to stay at home with the child awaiting his visa, without losing their own green cards. Another way to do it is to petition one parent, who then petitions the spouse with child as derivative (this is allowed for spouse of LPR category) once the first parent gets a green card. There is no way to bring them all together to the US at the same time your parents get their green cards.