American here. Whilst your husband was unreasonable to let you go down this path before slamming the brakes at the last minute, you really do need to reconsider.
NYC is crazy expensive. I know you’ve said that you’ve looked at housing…is that based on your own salary or on two earners? I don’t think it will be as easy as you think for your DH to get a visa. He has to get an employer to sponsor him. Coordinating two visas to start at the same time sounds impossible, particularly as it sounds like he doesn’t have any NYC interviews in the pipeline.
Your timeline is really going to mess up your 14YOs GCSEs. The US system is completely different—the GCSE and A-Level (14-18) years are mixed together. There are two semesters in each school year, with exams (“finals”) at the end of each semester. So that means a total of 8 semesters’ worth of final grades, which are averaged together to make a GPA (grade point average). These do not align with the GCSE curriculum AT ALL. Your timeline could have your DC being put back into a UK school literally months or weeks before their GCSE exams without the two years of learning the curriculum under their belt. This would be academic suicide.
We had a really good offer to take a job at an amazing place in the US, and it was a great job, but because of where my youngest DC was in their school timeline, it would have been detrimental to their educational outcome. So we passed on the opportunity. Sometimes as parents, we have to take these hard decisions. DH and I still talk about it 10 years on, but it was the right decision for our child’s education.
Also…have you looked at the schools in NYC? They can be appallingly bad, which is why many opt for private (another expense to consider).
And finally…the US is in a social downturn. Apparently the punishment for ignoring an ICE agent’s order to stop your car is immediate execution on the spot. These are very scary times. I thank my lucky stars that my DCs are UK citizens and that I am one too now. You couldn’t pay me enough money to move back to the US in the current political climate.