I like how diverse all three of your interviews were. Not only did you focus on different cultures, but looking at how parenting can be different between twins and adopted children as well gives us a wider scope to look at.
I wish you would have had time to focus more on the cultural differences of raising a child. From the bit that you wrote about it, cultural differences can be a bigger stressor that I originally thought.
What if you had interviewed each of your interviewees spouses? Do you think they would have found similar things stressful or do you think the two different people would have two different views?