parents GC application

hello, my parents plan to vist us in this Sept., and they will stay with us for about  6month. I will apply for my US citizenship by next Feb since I will have my GC for 5year by next May. So, my question are, could my parents file extension before I submit my citizenship application by next Jan? And, could I start their GC applications right after my US citizenship settled down? Any risk or any ideas? Thanks a lot for your advise.