The B can get the HK PR, just becasue papa or mama either one is Chinese citizen or papa or mama can prove that they are Chinese origin even though they are not HK PR. If not, the B cannot get the HKSAR passport.
per my understanding, the foreigner (non-HK PR) gives birth in HK, the B just can get a form ID 235B and birth certificate from the birth register. Then, they should go to the respective embassy to apply the passport.
Unless, the helper can prove that she is a 印尼華僑, or papa is a HK PR. So, the B can get the HKSAR passport.