Transfer iTunes balance?

Sorry for the loss.

and has a cash balance in his iTunes account

If you mean his Apple ID balance, see -> Check your Apple ID balance

Check your Apple ID balance – Apple Support (UK)

scroll to ⤵️

If you have Apple ID balance 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.

You also need this Apple article -> 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

Click here for more support and assistance.

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