Sorry for the loss.
1.
See -> How to request access to a deceased family member's Apple account
How to request access to a deceased family member's Apple account - Apple Support
2.
See -> Check your Apple Account balance
Check your Apple Account balance – Apple Support (UK)
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If you have an Apple Account balance that you can’t use
You can't redeem or return Apple Gift Cards, App Store & iTunes Gift Cards or unused Apple ID balance for cash, except as required by law. If your jurisdiction allows the refund of redeemed gift balances, you can contact Apple Support to request a refund.
When you contact Apple, include the following information:
• Your Apple ID.
• The refund amount.
• Your current delivery address.
Get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK)