Rhiannon Lavellan would be home-made cookies, slightly burnt. She tries hard, means well, and is very sweet. Most people like her, and she's great at parties. But she also has more than her fair share of screw-ups. As a bonus, Sera loves them cookies, even if it annoys her!
My other Lavellan would probably be grapefruit. She can be a little sour and hard to take, but she's also good. And she's a lot nicer if you take the time to sweeten her up.
Nico Cadash would probably be some kind of hard liquor, because you wince every time she opens her mouth. She also likes saying whatever stupid thing comes into her head, which people tend to do after a little to much of the drinking! And she can be pretty fiery, and since she's tiny, definitely liquor served in a shot glass.
I haven't played enough of my Adaar to decide, but probably something mellow, warm and comforting, but with a hidden edge. Hot toddy? (Enough with the alcohol!)