28 digit code

Hello ~ If the 28 digit code is a recovery key…

How to generate a recovery key - Apple Support*

*Using a recovery key is more secure, but it means that you’re responsible for maintaining access to your trusted devices and your recovery key. If you lose both of these items, you could be locked out of your account permanently. With that in mind, it's important to keep your recovery key in a safe place. You might want to give a copy of your recovery key to a family member, or keep copies in more than one place. That way you always have your recovery key when you need it.

~Katana-San~

If the 28 digit code is the iPad's screen unlock passcode, it has nothing to do with the iCloud account. The iPad's screen unlock passcode cannot be recovered in any way shape or form outside of remembering it.

You will need to restore the device to factory condition to remove the passcode. And set it up again. However you will need the iCloud email address and password used on the device if "Find My iPad" was turned on.

see here for steps to reset the iPad to factory settings: Link-> If you forgot your iPad passcode - Apple Support

To recover the iCloud password, you can start here: link-> If you forgot your Apple ID password - Apple Support

If your husband has another device, iPhone, Mac, etc.. that is using the same iCloud account, you may be able to use that to reset the iCloud password.

If not, then you will need to put in for an account recovery procedure: link-> How to use account recovery when you can’t reset your Apple ID password - Apple Support

If you don’t have the Recovery Code that you generated (noting that you will have seen dire warnings of needing to keep safe), have lost your AppleID credentials - and have also lost the the paperwork that demonstrates that you are the original owner - then you are clearly in a very difficult place.

As is, you are indistinguishable from those that are perhaps less than honest. While contributors here will sympathise with your predicament, in absence of you being able to self-resolve your issue, Apple that will require proof of original ownership. Per your description, this cannot be provided.

As a consequence, you may be unable to recover use of your iPad. Perhaps take some solace in knowing that an older model iPad will very likely not be able to run recent Apps - and may even be outside of update support and therefore approaching obsolescence. If so, perhaps replacement is more constructive channel to pursue.

Not sure what 28 digit code you’re referring to.

If he doesn’t remember the password for his iCloud account, he should start here: https://iforgot.apple.com