SeverusProsper - This is... gutsy. I think just about everyone will associate Severus with Professor Snape, although pre-Harry Potter I imagine this name would've been quite bada$$. Personally, I don't think Prosper belongs on a person--it sounds like a command. So... sorry, not feeling this combo.
JohnAlexander - Both names are pretty "sane," but I imagine that there are *many* other John Alexanders in the world today.
HoratioNelson - Not terrible, actually, although I have a personal aversion to Horatio and other like-sounding names (due to the first syllable).
FrederickGeorge - Sounds quite like the younger brother of a Count in Late Victorian England.
EdwardLawrence - I really like this one! Both names are familiar, but not too common, with a touch of sophistication. I like it a lot!