I imagine in those cases the government can and will force any airplane in American soil or airspace to act like this, whether they are owned by an American or foreign corporation.
Your imagination is not realistic. There's no legal way to require foreign pilots who are citizens of another country to follow US government orders. And it's not possible in the short term to put US pilots on those airplanes because each airline has a unique combination of airframes, engines, and avionics. Plus if the maintenance and logistics infrastructure aren't located in the USA then those airplanes would quickly become inoperable.
A foreign airline operating domestic routes in the US would likely use many US pilots/employees.
Sure for a minor incident. But any foreign airline would immediately move their planes out of the US if war broke out. And there would generally be warning signs before it happens, giving them plenty of time to discontinue flights.