Certain name pairings for siblings? Any patterns noticed?

[mathanxiety]

I know families with the following combination of names:
Sam and Max -- 2 families
Sam and Charlie -- 2,
Sara and Rachel -- 3,
Sara and Emily -- 2,
Kathryn and Elizabeth -- 2,
Michael and Grace -- 2,
John and Thomas -- 2,
Maggie and Katie -- 3.
Has anyone else noticed any patterns where you can pretty much predict what the second child will be named based on the first child's name, or do I just know a lot of people who are not capable of an original thought when it comes to naming their babies?

I can see the link between John and Thomas - I know a lot of families with these names, probably as they're both biblical names. The other pairs surprise me though!

similar thread here