What are your DC’s reasons for not wanting to go?
14 years is a v difficult age to move to a new school in a different country for numerous reasons. It’d be hard enough if your DD was excited to go. But if she’s not keen, it’d be even tougher.
Then, it’s not a long-term move. You plan to move back to UK after 18 months. So, even if your DC cope and settle well, they’ll have to move again. Would they be able to return to the same school in London or have to wait ages for a place to become available? Would they continue with their curriculum (e.g. international school) in US or be in US education system. If the latter, they’d miss two years of English school content. Not to mention the impact on friendships, which are key at those ages.
It appears v disruptive to your DC, who should surely be both your priority. Did you and your DH consider the impact on, and feelings of, your DC before you considered applying to work abroad for a lengthy period? Did you discuss it with your DC before you applied?
Maybe your DH won’t discuss reasons as he thinks it’s obvious. But he should explain himself, i.e. why he was happy for you to apply. Maybe he thought the chances of you getting the role were slim, so it wasn’t worth discouraging you. If so, probably not the best approach, given the outcome.