What are the steps necessary to repossess a motorcycle you financed for a family member in Georgia?

depends on what state you are in.

None, she and her husband are dead.

No, not unless otherwise related by blood or marriage.

A notary only validates that a signed document is signed by actual person.

It is okay to do it in most circumstances, but it is questionable if the document benefits the notary. Such as notarizing a quit claim deed to the benefit of the notary would not be a good thing.