Child travel with grandparents only consent letter

My child will be travelling to Guangzhou with grandparents and Family members but not with husband and I. I am going to prepare a child travel consent letter and a photocopy of her birth cert. My qn would be, does the letter has to be by lawyer and do I have to provide husband's birth cert to prove grandparent's names? Hope someone here is able to share experience or know the answers. Thank you