I'd go with neither. You're going to date her. Both names are very popular right now and I know three other Kennedy's that are 3 or younger. In the late 80's when The Little Mermaid came out everyone named their daughter Ariel. How cheesy would it be now to be 23-25 years old and be named Ariel?
As far as naming all the kids using even just the same first letter, why? Give her her own identity. Something that she can call her own.
Just my 2 cents worth... OK, maybe just a peso or so.
Oh, and both names are so stripper names.
First name similarity is a fluke. Brooklyn is what we had chosen but it just does not seem to fit. Kennedy is the other name we like. It will be one of the two.