Step-children visa rules, family visa

My husband is looking at a work opportunity in China but we are interested in the family entry permit rules for blended families. I hold a New Zealand Passport, as does my son from my first marriage. My husband holds an Australian Passport and we have a son together who holds an Australian Passport.
As my husband is not the legal parent of my older son, can he sponsor him under the family entry permit rules?
Thanks for your help