I am very sorry for your loss.
Unfortunately, since it is clear you will be unable to obtain the needed password or answer the pertinent security questions, we can do nothing to help you, except to mention that Apple Support will help you if you have a court order instructing Apple to assist in the provision of access to a decedent’s information from the deceased person's accounts. (See How to request access to a deceased family member's Apple accounts https://support.apple.com/en-us/HT208510.) Note that this process won’t work everywhere.
If you want to contact Apple support to discuss your problem, see the support options below. Alternatively, if an Apple Store is open in your area, then you can go there to deal with your problem. In this case, you can make a genius-bar appointment (https://www.apple.com/retail/geniusbar/) if you want.
Get a call from Apple support to help solve your problem using this
link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362
Apple ID Support https://support.apple.com/apple-id
Apple ID account security for country-specific and
region-specific help https://support.apple.com/en-us/HT204169
Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.