If they will stay < 6 months, they won't lose their GC.
If > 6months and < 1 year, they need a good reason to explain why they have to live outside for such a long time - schooling, medical treatment, etc.
If > 1 year, you need to apply for a re-entry permit for them before they leave US.
If > 2 years, their GCs are gone, generally.
By the way, they can't apply for AP anymore after getting GC.
If > 6months and < 1 year, they need a good reason to explain why they have to live outside for such a long time - schooling, medical treatment, etc.
If > 1 year, you need to apply for a re-entry permit for them before they leave US.
If > 2 years, their GCs are gone, generally.
By the way, they can't apply for AP anymore after getting GC.