From so many vantage points, it doesn't really matter if the adoption was international or domestic. First, domestic (non-private) and international adoptions have lower rates of comprehensive prenatal health care and FAS. The situations are much more tenuous and poverty (access to healthcare, nutrition, vitamins, etc) is a huge issue in many domestic and international adoptions. In international adoptions a potential issue for development and bonding comes in the form of children living in an institution with less than adequate caregiving compounded with inadequate prenatal care. For those who have asked, yes, adoptive parents are counseled about potential issues that can and do occur. That said, when you are wanting a baby (through pregnancy or adoption) you never think you will be the person to miscarry, have a child with a genetic anomaly, or adopt a child with unknown health/developmental issue. Adoptive parents start out like biological parents--thinking about the great and wonderful aspects of raising a perfect and wonderful child. People who adopt children with disabilities (even those who adopt with some known disabilities and get surprised by undiagnosed ones) are also counseled-- but again many APs think they will get the lesser disability or consequences of a disability. So, yes, we know but we dream just like all parents do.
My understanding is that this family took custody these boys when they were days old. If his brother is bio to him and was in custody at two days old, then it is impossible that this was international. Children in international adoptions (back then in differing ways than today) have to have paperwork that proves abandonment, health certifications, etc. There is no way a two day old or very young infant would be able to enter the US that quickly-- four months was incredibly young (and, exceedingly rare) back in the late 1990s. If the bio or half-bio is correct and if the two day old photo story is correct, they had to be born in the US. I have experience with international adoption, many adoptive parents would give their eye teeth to hold their child at 2 days or a week old.
Biological mother drug use, stress level (including trauma related to trafficking or rape), access to care, maternal mental health/functioning, and generational care are all factors in delivering a healthy baby. When factors for an optimal pregnancy are compromised, a baby can be born with health or developmental issues. If that same baby is born with drug related or alcohol related withdrawal issues, we have prenatal factors and newborn factors to contend with. All of a child's issues are compounded if their placement in a home is erratic or changing or chaotic-- ie, with a parent who is unable to care/provide for them in love/food/shelter, a foster home with many children with many needs, or an orphanage with too few caregivers or too little food. Yes, adopted kids can be at a greater risk for mental health issues but stable, consistent homes with parents who are well counseled/educated can overcome lots just as children born to parents who don't have enough food or shelter, struggle with providing love, maintain chaotic homes, etc can be at great risk without every entering the realm of adoption.
Hope this tome helps those who are asking about country of origin or know about the adoption nightmares and are wondering about parallels.