Hello,
Make sure to have the names on Chinese characters preferred in old documents and have the name of the Guangdong province (canton) where he lived, the Chinese government has a department where they register the household and the name a date of birth of its family members (only direct dorm the male side) so, make sure you have his last name right and good luck. Oh once you have the name and place, city or region where he lived, have a trusted translator who knows mandarin and Cantonese and set a mont or two months trip to China. Don't do it on phone 'cause you'll be ripped off
Good luck!