Inherited deceased brother's iphone, will I be able to use?

To be clear, you will not be able to access the data on the phone. That data is encrypted with the Passcode and Apple does not know what that is to unencrypt the data. The options referred to in the article are:

• Remove the Activation Lock on the device. This will erase the device and allow it to be set up by someone else.
• The account data that you can access is what has been stored in iCloud. This can include photos, email, notes, backup, etc. If there is a backup there, that is the closest thing you will get that will have the data that was on the phone.
• And lastly, you have the ability to delete all data stored in iCloud.

Re: “When the account has been deleted, will that unlock his phone and give me access?”

No. Deleting the account before removing the phone from the list of devices associated with it might make it impossible to ever reset and use the phone.

No. Do not have the account deleted before removing it from the iPhone. Deleting the account will not magically unlock the iPhone.

If you delete the account before removing it from the iPhone, the iPhone will be rendered unusable.

You request access to the account, so that once you restore the iPhone to factory settings, you can enter the account email and password in the Activation Lock Screen to release the iPhone from the Apple account so it can be used.

The data on the device itself cannot be recovered without the passcode though.

Removing the account will not erase the iPhone at all. You must erase it before you can remove the account.

click here ➜ How to factory reset your iPhone, iPad, or iPod touch - Apple Support

then here ➜ How to remove Activation Lock - Apple Support

See: How to request access to a deceased family member’s Apple Account - Apple Support