I am very sorry for your loss.
But, you won't be able to get anywhere with your quest if all you have it the old number. But, you can contact Apple Support to discuss the matter additionally if you want. Note that Apple support will help you with your problem if you have a court order instructing the Company 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.) See these support options:
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 Be patient. Sometimes Apple phone support is not available.
Apple ID Support https://support.apple.com/apple-id
Apple Support Twitter https://twitter.com/AppleSupport There may be an hour or so wait.
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.
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Alternatively, if an Apple Store is open in your area, then you can go there to deal with your situation. You also can make a genius-bar appointment (https://www.apple.com/retail/geniusbar/) if you want.