They will require a Visa, obtained in HKG (or any Chinese embassy) before departure. Rush and Express options available at a price.
DIY in HKG at the Visa Office in Wanchai.
Address/Office hours/Enquiry service It's a circus. Queue jumping, long waits, etc but it's at cost price.
You can have someone else do the work for you (travel agent or 'China Travel' at 50 to 150% mark up.
If your family member has a HKID they are eligible for a multiple entry visa. Take the original, a photocopy, the passport that has their HKG employment visa and a photo.
Good luck.