Why longer than 90 days? That is a long term visa. If a bank won’t open up an account with that then it’s probably because they can’t be arsed to deal with he paperwork- especially if you’re American.
It’s not too difficult to do yourself if you meet the financial requirements.
You’ll be better off to apply for a Non O visa prior to coming here because it’s far easier to open a bank account with a long term visa over a tourist or exempt entry.
The Non O is valid for 90 days from issue and on entry you’d get a stamp for 90 days.
Open the bank accounts and deposit the 800k (each) and when that’s been in the account for 2 months apply for the year extension.