Dependent on Family Based Petition

[L1_to_H1]

Hello,

     One of my relatives (US Citizen) applied for family based GC for their married brother (A) (who lives in India). The priority date on their application is current. Now the brother's kids are close to 21 years of age and they want to avail the GC just for their kids. What would be the right way to go about it ? I have following questions:

 

1. Does A need to travel to US and start the GC process for himself before the process for kids can be started? Or can kids travel alone and start the process independently?

2. Do they need to stay in US for whole process duration or can they leave once 485/AP is done? How long does 485/AP typically take?

3. Once they leave US after getting GC do they need to submit an application which allows them to be out of US for a long duration without abandoning the GC?

4. If A needs to get the GC before kids can even apply what happens to kids GC if A abandons his GC later on ?