With a Kaylee, I wouldn't have use the spellings Emilee or Ashlee, but the traditional spellings (Emily and Ashley) work well with Brandon and Kaylee.
I also like Caitlin/Caitlyn with Brandon and Kaylee but again, I wouldn't go with an unusual spelling.
I agree with the spelling issues. I don't like Emilee anyways, though I think Ashlee is ok, but not with Kaylee. Emily and Ashley do still have that same ending as Kaylee so keep that in mind.
Katelyn (I prefer it with one "n") or Caitlyn/Caitlin doesn't but does have the "k" sound at the beginning which also makes it matchy.
That being said, Ava is my favorite of your list to add to your sibset.