I agree that this thread has been fascinating and given me lots to think about. Younger son’s girlfriend is from Hong Kong and has visited us for various holidays for the last four years, and for longer visits more recently. Making her welcome means that we see more of our son. I really enjoy her and have no real complaints about her, though she probably doesn’t help with food prep/cleaning up as much as an American might. She does help some and I will say it’s partly because she’s taking cues from my son, who also doesn’t offer as much help as he might either. We’re in Hong Kong now and have gotten to know her parents quite well. They are lovely and we have lots in common. When in the course of a conversation they talked about how each of the girl’s had their own nanny, I thought secretly to myself, well that probably explains a lot! (I spent a good part of my childhood in Africa, so I’m pretty aware of the contrast of having a million live-in servants to none.) Anyway, as far as I can tell we have a good relationship. I’m surprised in a way that both with her and her parents I haven’t felt more cultural differences.
As I think about DS #2’s wedding, which we paid for entirely (due to her parents’ divorce and father’s bad financial choices), DS thanked us profusely, but I don’t recall DIL doing so. But TBH, I don’t recall. Son is so appreciative and seems to be even more effusive since the wedding, its a nice bonus 
Regarding advice, I finally figured out how that should work when DD went to university. I don’t give advice, it’s not my job to fix their issues. It’s my job to be a good sounding board, to give them things to think about so they can make an informed decision, not make the decision (heck I don’t want to be blamed for it!)
That felt much better to me and I came right out and said it to the kids, you do you, but use me for my experience so you make YOUR best decision with as much info as possible
I also strongly encourage the kids to appreciate the different family cultural differences. Our kids are quite close and hold our family in high regard, I want them to respect other ways that other families do things, and I think the do. As teens it felt like they got into a place of judging people who did not do what we did and I made a real effort to open their eyes to there being many ‘right’ ways to do things. It seems like it’s working.