I fear that I'm going to be entirely too bland, and frankly I'm not a fan of many of these names, so my suggestions are likely not going to be all that interesting.
Girl:
Susanna - I like this name a lot (tend to prefer
Susannah, but that's a small point of personal taste) and think it requires something that feels similarly old-style-but-not-outdated.
Susanna Abigail might be a bit Puritan-esque for some, but that's where my head goes. (I also have a think for
Susanna Eleanor, nicknamed
Sue Ellen.)
Antonia - Eek. I don't like this one much. I'd go with something short.
Antonia Jane might be bland, but it works for a name I don't care for.
Christina - My usual inclination here is
Christina Maria. It's a little sing-song-ey, but I think it works.
Kessie - I'm not sure what this is - it's sounds like something you name a pet bird, so I'm not going with it.
Marigold - Eek. I'm not even sure. I find the upward trajectory of this name disconcerting.
Vienna - I dislike city names without some significant attachment. I've got no ideas here.
Holly -
Holly Katherine. I think you need something a bit longer -
Holly is dated name to me but I do like it. I think it requires something to move it from a dated trend to something more sophisticated. I know some view
Katherine as overused, but I think it's been so widely used for so long because it does have a certain regality to it. (Actually I'd go with
Katharine, that's my favorite spelling.)
Claudia - this is one that I think works with something short OR long. So, I could see
Claudia Alexandra being pretty, or
Claudia Jean.
Boy:
Harvey - I've always thought the name
Harvey sounded like a dog's name, and I also associated with hot dogs for reasons I can't explain. Give it something that gives it a greater air of seriousness.
William, maybe.
Walter - If you're going with something that's this old-sounding (though, I think, usable), go with something classic and sturdy, like
Walter James.
Leon - Another name I don't like much. Maybe
Leon Anthony?
Leon Alexander?
Ichabod - Oof, this has such singular connotations that I don't know. I can't imagine something naming their child
Ichabod WITHOUT some deep tie to
Washington Irving, so why not go all the way with
Ichabod Washington?
Andrew
put a smile on your face - make the world a better place (: