When they applied for their visas the 2nd time you should write a letter to cover their TRAVEL PLAN and make it very clear that your parents visited here 3 years ago, they returned before their visas expired and you will make sure that they will return to China before their visas expires if they come to visit here again. You should also write that you visited your parents a couple of times between ..., you meet with your parents every year(?). This time you would like to show your parents around ... (the TRAVEL PLAN).
Write to your parents about the plan in Chinese and tell them to bring the letter with them when they go to see the VO.
Good luck!
Write to your parents about the plan in Chinese and tell them to bring the letter with them when they go to see the VO.
Good luck!