Hi
There are no straight forward answers to your questions. All are dependent on the results of the statutory residence tests.
1 - Your husband will need to review the guidance for and take the statutory residence test, to determine his residence position. Only then will he know what course of action is required.
2 - Your pay arises in the tax year 2023 to 2024 and is taxable in that tax year
3 - You will need to review the guidance for and take the statutory residence test, to determine your residence position. Only then will he know what course of action is required.
4 - Both you and your husband will need to review the guidance for and take the statutory residence test, to determine his residence position. Only then can you consider whether split year treatment applies. If it does, then a self assessment tax return is required to claim split year treatment.
5 - Yes, their bank interest will be taxable in the UK and would be reported on a self assessment tax return. They will also need to consider the statutory residence test, to determine whether they will need to declare that element of their interest arising in the part of the tax year they were not in the UK.
The guidance and statutory residence tests can be found at
RDR3 Statutory Residence Test, as well as guidance on split year treatment.