In the first place, they are not namesakes unless one person was given the name because the other person had that name ('sake' means 'purpose or reason'). So your case 1 seems unlikely because the name is so common, while case 2 is unlikely because we inherit surnames, we are not given them. However, your question makes sense, but they would all be 'namesakes', with context making it obvious which parts of the name were meant.
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