بسم الله الرحمن الرحيم
(Fatwa: 1138/395/TL=9/1434)
In the case mentioned above, when the condition of America is extremely unpleasant and it is sure that the children will be affected by the culture if they are shifted there, then your brother in law should not take such initiative. If your brother in law does so and ultimately the children leave Islam or involve in sins, your brother in law will also be responsible. It is the duty of parents to give the children good name and proper education and upbringing:
قال رسول اللہ صلی اللہ علیہ وسلم: من ولد لہ ولد فلیحسن اسمہ وأدبہ فإذا بلغ فلیزوجہ فإن بلغ و لم یزوجہ فأصاب إثما فإنما إثمہ علی أبیہ
“Whoever has a child, he should give him good name and upbringing. And he should be married when he reaches his age. If he reached his age and was not married and he committed any sin, then his father will share the sin.”
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband