Unable to update my iphone Ebay app

It sounds like the app on the device you were using was downloaded using his account. Apps are permanently linked to the accounts used to purchase them. You need to delete the app entirely and download it with your account.

Family Sharing of apps is also possible but since he is deceased his account should no longer be accessible for the purpose of sharing apps.

For information about how to request access to a deceased family member's Apple account data, and possibly their equipment, read this support article --> How to request access to a deceased family member’s Apple Account - Apple Support

Legal - iCloud - Apple

IV. D. No Right of Survivorship

Except as allowed under Digital Legacy and unless otherwise required by law, you agree that your Account is non-transferable and that any rights to your Apple ID or content within your Account terminate upon your death. Upon receipt of a copy of a death certificate your Account may be terminated and all content within your Account deleted. Contact iCloud Support at iCloud - Official Apple Support for further assistance.

Please follow this path,

iPhone > Settings > whose name is at the top of the page?

Where is the update failing? Can you delete the old app? Can you download a new app? Can you login and out of your account on the app?

Do you and your husband use the same Apple Account (formerly Apple ID)?