Marriage visa

I assume you m,eans a family reunion visa (for joining your spouse after marrying), not a marriage visa (for attending a wedding in Germany).
In addition to being married to your German spouse, to get a family reunion visa you also have to show sufficient financial reserves for the two of you (this might be difficult if both are not working), enough living space (e.g. rented flat), a German health insurance and basic knowledge of German language (A1 level or higher).

Yes I mean family reunion visa what if he gets a student house and per time job?

It must be sufficient money, minimum €8820/year per person, and space for the two of you, usually around 60sqm.
A part time job and student apartment is not enough for two people.

I have question about marriage visa too.... I'm currently still in HK and will apply the marriage visa once I get the marriage registration confirmation letter from Germany which is likely to be mid-May. However, I booked the flight to leave hk end of June. I saw that for marriage visa, I need to leave my passport in HK for visa process, but since I have already booked my flight and need to be in Germany for his mother's surgery, I was wondering whether it will be ok for me to use my other British Passport to travel to Germany during that time.

I can't find any news / anyone to help on this matter in HK😢