Offialy your extension ended on the day they passed away. But immigration will not know about it unless you inform them.
Before your extension expires you will need to leave the country and enter with new visa.
She can apply for a extension for being his wife.
Her extension will be valid to the day his extension expires.
There is no minimum age for the extension.
You only need to prove the monthly tramsfers by showing a one year bank statement that shows the funds came from abroad and a letter from the bank confirming your account is valid.
Info is here on embassy website.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://th.usembassy.gov/u-s-citizen-services/passports/adult-passport-renew/&ved=2ahUKEwjN2fjX6az8AhVuCLcAHU_QAIkQFnoECBoQAQ&usg=AOvVaw3fq42r9Ms28z4tux6L8_6l