I am re-editing this post hoping to convey the sense of my request:
This recent question has been closed as a duplicate but IMO the issue appears to be still open and needs a more definitive answer.
All evidence I found and posted in my answer suggest a clear rule about the pluralisation of family names ending with a "y".
But there are some interesting upvoted comments which support a very different view and suggest a much less prescriptive usage of the rule mentioned.
Though the comments are not supported by any reference, they are relevant and can actually be the basis for the type of answer OP is looking for.
Should the question be reopened or should the OP ask a new question? A bounty on the old question doesn't make sense in my opinion and the new one cannot be the object of a bounty for obvious reasons.
Whatever the case, I think the question still needs attention and whether or not the issue is just a question of personal preference should be made clear to the OP and other users.