Longtime lurker here, but I can give a lot of insight into moving countries as I moved countries 7 times by the time I turned 16, and although I went to school in each country, I only stayed in a school for two years maximum and even then, I struggled socially and emotionally since I barely had any friends throughout my childhood, it got to the point where it was incredibly detrimental to my mental health that I developed a personality disorder. It took me until I was 20, nearly 21, that I was able to function a lot more socially and emotionally at the level my peers are at now, but I will never forget watching movies where the main character had a friend or even a group of friends and it really broke me down because I realized I had no one. Even now, I really wish I had normal teenage experiences (Halloween parties and NYE parties) and I am resentful of my parents for putting me through my childhood. I am incredibly terrified to have a birthday party with my friends because I'm still scared I have nobody.
I can't imagine what this is doing to Mia and Sienna and how this is all going to turn out, but I know eventually they'll suffer once they become adults and they will be so far behind their peers that they probably won't have many friends their own age.