If either taxpayer revokes the election, as of the first taxable year for which the last day prescribed by law for filing the return of tax under chapter 1 has not yet occurred. "
I have underlined the words of import to me --- I interpret this to mean that the termination of the 6013(g) election need to be made for the year before the due date of the filing AND during that year. Therefore my suggestion would be to include the "termination of election" letter during filing of 2024 return. Once terminated you cannot re-elect to be under 6013(g) again ( the statute does not say how long is the blackout period ).
At the same time I do not see any harm in filing the termination of election at any time during 2024 -- just make sure that this termination is effective first of 2024 i.e. for all of 2024 tax year and beyond..
For 2024 , your husband recognizing the interest income in full while filing his 2024 return, is the correct way to deal with this income.
Note that as a NRA ( Non-Resident Alien ) even with a Tax ID ( TIN ) but with no connection to US or No US sourced income, you are not required to file a US return.
Here is a link to section 6013 --> 26 U.S. Code § 6013 - Joint returns of income tax by husband and wife | U.S. Code | US Law | LII / Legal Information Institute (cornell.edu)
Is there more I can do for you ?