Q: how can i backup a reset the iCloud account of somebody who dies?

Apple's Terms of Use for iCloud say:

No Right of Survivorship

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 www.apple.com/support/icloud for further assistance.

Basically you have no rights in his account: if you know his password you can enter the account and retrieve personal data to use elsewhere. If he had purchased music, films or apps in iTunes you cannot transfer these to your own account.

If you don't know the password it seems doubtful that Apple will allow you access to it. However as far as all these questions are concerned the authoritative answers must come from Apple so you will need to contact them as indicated above.

Sorry for your loss.