Just to make sure I understand it correctly:
(1) If they stayed in the US, they would not be penalized for overstaying when I apply GC for them. I.e., overstaying is irrelavent to GC application.
(2) However, if they go back to China after a 180days or more over stay, they will not be able to return on B-2 visa for the next 3-10 years.
(3) Not clear to me is what if I apply GC for them while they stay in China after an overstay.
Agains, thanks for your help, look forward to hearing from you.