Hadley & Caroline: Hadley is unisex and more masculine than Caroline. If Caroline was more tomboy and Hadley more feminine, it would seem strange. I think that one could be envious of the other, because of the opposite ends of the spectrum that these names are on.
Haven & Hadley: I like that they're both unisex names. I prefer Haven over Hadley. I don't like that Ha- sounds are pronounced differently. Hay-ven and Had-lee. The names are also rather similar because of the Ha beginnings.
Hadley & Kirrily: I prefer Kirrily even though I'm not sure how to pronounce it. I think that Kirrily may present spelling problems. I don't like that both end in "lee". This combination is my second favorite combo.
Hadley & Sage: I prefer Sage over Hadley. I like that both names have a nature vibe. Hadley seems stronger despite the lee ending.
I also really like "Kirrily & Sage" and "Haven & Sage".
Hadley: I've always thought of Hadley as "had lee". As in he had lee over for dinner. I also knew a very manly man named Hadley. He sort of created this male perception of the name.
Thanks for the feedback! I do love some of the combos you suggested but I really wanted to find a good match for Hadley. I've loved it for a long time. But I'll have to consider sage and kirrily and haven and kirrily!