From what I understood at the time, immigration would need to see a letter as well to let him take kids out of Taiwan, which, I hate to say because it is going to sound bitter and biased, would probably be next to impossible for him to do but perhaps easy for his Taiwanese wife.
There was enough evidence of corruption and bias on the court’s behalf in my case that I would fear for any fairness on his behalf (e.g., I had secretly recorded an assigned-by-the-court’s Guardian ad Litem’s visit to my home in 2016, yet her report nine months later ripped me apart, stated all sorts of absurd falsehoods, alleged so many lies. Then both the custody judge and appellate judges used her report as the reason for me to lose custody, and then they defended the cu-- of the woman for her professional, respected status as a university prof, even though my secret recording of her visit destroyed every single false claim she had written).
Anyway, during those 3.5 years in court, I had promised my ex that I wasn’t going anywhere with the kids, proving also to the courts that because she had the kids’ Taiwanese passports (which had their last entry stamps from our trip to Brunei) I could do nothing at all with the kids’ US passports which I had retained in my possession (i.e., since there were no entry stamps in them, we wouldn’t have been able to leave). Moreover, at the start of the separation, since things were fine for 2-3 months, I had it also in my mind that I never would have taken my kids away from their birther (I refuse to use the word ‘mot—’ with her), for that would not have been fair to my children.
Wishing the man well.