This story really hits home. I'm close to your wife's age and I also lost my father suddenly 2 years ago. I'm not Chinese but I'm from a very traditional culture where family can be quite complicated and there's a lot of emphasis on "duty". There are definitely a lot of similarities to what you're describing in terms of family dynamics.
My own mother (who also lives in a different country) is very manipulative, controlling and can also be emotionally abusive. She also places a lot of (unreasonable) demands on my fiance about being the "provider" and her expectations of him as her future son-in-law. When my dad died she even said something very similar about him having to step up as "the man of the family". My widowed grandmother was very controlling of her and was unreasonably demanding of my father and sometimes I feel like as she gets older, she's just determined to let history repeat itself.
When my dad died, I went through a period where I was basically at my mother's beck and call. I blew through a huge chunk of the money we were saving for a house on last minute flights etc because she would be not coping and I'd drop everything and go to her. I felt like I had to put everything second place to her and her grief and that I had no right to complain because she'd just lost her husband. I also had a lot of pressure from extended family to "look after her".
It was killing my relationship. Everything in our lives got eclipsed by my mother's expansive and all-encompassing grief (and at no point was I even permitted to grieve for my own loss without the implication that I was being selfish). My SO ended up getting shoved to the background and just expected to provide limitless support without complaining. She would come to stay and it would be a total shitshow - I could write all day about the stuff she did and said but the bottom line is that she's overbearing to the point where our lives weren't our own.
Eventually I had to make a choice - be constantly at my mother's beck and call and lose my SO in the process or grow a pair and start setting boundaries. It's incredibly difficult when there's a death involved because you know that the other person is grieving and you feel like the world's worst daughter for taking a step back and drawing a line. I actually had therapy to help me get to the point where I was able to overcome years of conditioning and actually start interacting with her in a reasonable and healthy way.
We started limiting visits, stopped taking the constant 2am phone calls and started gently but firmly pointing out when she'd crossed a line. Things aren't perfect and she still gets out of control but my SO knows that I have his back now and that I'm not allowing things to spiral out of control.
If your wife doesn't take action, she is going to end up destroying your marriage and perpetuating a very unhealthy environment for herself and your son. It’s not going to be an easy conversation to have - when my SO first raised things with me I reacted very badly and felt like he was being selfish and didn't understand. "My Dad is dead, she's lost her husband - how can you be so callous?" was pretty much my standard refrain. But actually, he was right, the situation was a mess and I'm glad I got help to address it. I would have been beyond miserable if I'd allowed things to carry on the way they were.
Maybe I'm projecting here but I'm betting that your wife is also unhappy. And I'm willing to bet that she's allowed her misplaced sense of duty to prevent her from grieving properly herself. And I would strongly encourage her to speak with a professional and work through the mess of emotions she's probably feeling. It might be messy but it's OK to put your foot down here, OP. She may very well thank you for it one day.