One Customs decarlation form and one FinCEN 105 form for both your parents.
See:
https://help.cbp.gov/app/answers/detail/a_id/441/~/travelers-eligible-to-file-a-joint-or-family-declaration-on-a-cbp-form-6059b
• 太謝謝了,太麻煩8老師了 -三問- ♀ (0 bytes) () 02/29/2016 postreply 23:32:00