Yes, this is an oldie but a goodie and it just keeps coming back.

Is there any way to prove which credits belong to (mainly) director Aman Chang and which to actress Cheung Man ?

They have precisely the same name.

Sharla's credits on hkmdb currently include Production for Dream Lover (1995) (also the presenter, a credit I am just about to add) and Writing for The Stand-In (1987).
I have no firm proof, but I always thought she did only acting.

Given the photo of Aman Chang, he looks a bit youthful to have been responsible for the production of Dream Lover, but perhaps he has those Ron Howard genes .........

Can anyone authoritatively state that Sharla does or does not belong to these non-acting credits ? If not, I'd suggest that we have a 5th and maybe even a 6th Cheung Man to deal with. Gawd, perhaps they should start their own secret society.

No, I think Sharla was really the producer and presenter of "Dream Lover".

Sharla was friend of producer/director Gordon Chan, they worked together in several movies. But as far I know Gordon and Aman Chang never worked together.

Also, the production company of "Dream Lover" is "[Sharla] Cheung Man Prod. Co.", which also produced "Romantic Dream" starring... Sharla.

[The problem here is that the assistant director of "Dream Lover" is "Cheung Man", so it can be Sharla (who never was assistant director) or Aman... ]

About "The Stand In", I am sure Sharla did not write the script, but another person actually called Zhang Min. I think one of our editors "created" many mainland people using their cantonese name instead of the mandarin name.