@MagsMaggie
Once you admit that you do not own a name, the need to be that invested makes little sense.
Rarely are there names that someone else somewhere have used. In classrooms on jobs etc, there are often several people with the same names, and nothing major or monumental happens because of it.
In my opinion, as adults people rarely appreciate the cutsie or unique effects at spelling that parents engineer in their efforts to be different or creative. Kids often seem to enjoy being able to find personalized items with their fairly common names on them.
Given that you don't own a name, I don't think that a head's up is necessary. If you are friends it maybe the kind of thing that you talk about in the course of normal conversation, but many people prefer not to mention actual names until after the birth.
In our immediate family, we have. 3 Jonathan's and 5 Matthews and no one gets upset or confused. Too many more important issues about which to be concerned.
Your son probably won't care. By the time that he is old enough to be aware, shared names, both dates etc, will likely be an commonplace experience for him. He may even enjoy not having such a unique name all to himself.
O