My GF and I were due a week apart. In the end we agreed to discuss our chosen names shortlists (had spoken of them to no one else) and it turned out we both liked a variant name. I like Tobias, she liked Tobiah. In the end, we agreed first across the line got to pick their favorite. Anyway, she had a boy and I had a girl and that sorted that out.

So I think you should talk about it with your friend. In a shortlist kind of way. Decide between yourselves what's ok and what's not ok. In real life, you're just as likely to make a new friend who ends up have the same named children, so does it really matter in the long run?