My opinions only:
1) Should be fine as long as your F2 visa is still valid.
2) Why did you get denied when you tried to change your status from F2 to F1
in the states? You need to find out the reason and tackle it.
3) Should be similar. You can try to get F1 visa in China since your change
of status attempt failed in the states. Make sure you have sufficient
financial support to finish your school.
4) Shouldn't be related. Your mom can still come here as long as she has a
good record.
