Family visa for daughter more than 21 years old

[paulem]

One of my aunt's family applied for family green card by her brother long time back.Now they are processing the case.When the case was applied both the kids of aunt were less than 18.Now when the case is conisidered daughter (un married), is less than 24 years old.

1. Is there anything they can do to bring there daughter also with them
2. I heard from somewhere that , if only one person in the family is left out and the person is less than 24 years old , then they can file a petition in the court .Is there such a rule
3. if they can file a petition , how long does it take to get a decision and what are the chances of getting a favourable reply