*Spoiler ahead* I think the real Painter is actually Ng Sau-ching. Hear me out:
There are only two possible Painters, who are Ng Sau-ching and Yuen Man. If the real Painter is Lee Man, it's impossible for Uncle Yam to talk to him like in the ending. It also wouldn't make sense to have their production right next to an artist's studio, because it would be too obvious for Yuen Man to figure out.
However, if the Painter is Yuen Man:
1. Why would she bind up her own fiance?
2. Why would she threaten to kill the woman on the bed, who would then be Ng Sau-ching, when she doesn't love Lee Man? Lee Man is the one in love with her, but it doesn't make sense that Yuen Man loves him.
3. Why would Lee Man look at the woman on the bed in the hotel, after everything collapses? Shouldn't he be looking at the person he cares the most about, the one he loves which is Yuen Man?
4. Why would everyone in the gang obey Yuen Man, if it's clear that it doesn't make sense to bind up her own fiance on the bed? Then, wouldn't they figure out that the woman threatening Lee Man is actually Ng Sau-ching? In that case, they should be turning on her.
But, if the real Painter is Ng Sau-ching, then it makes sense why everyone was listening to the woman threatening Lee Man.
Also, I think the one who sent Lee Man to jail was Yuen Man and the one in the end in Yuen Man. He really did get rescued by Ng Sau-ching.