Im a UK citizen, hes from the USA. We will be applying for the spousal visa to move to the UK.
First, hubby: if he is earning income whilst resident in the UK, he will have to pay tax to HMRC (the UK IRS). As for the IRS, the US will tax all US citizens no matter where the income was earned. So, he will file a tax return to the UK as it has primary taxing authority, and to the US because it has citizenship based taxation. That includes
all earnings, including savings, from everywhere (US and UK).
As a UKC (and not a USC), do you have a green card for the US? If so, how long have you been permanently resident in the US and do you intend to keep the green card when you return to the UK?