I am expecting fraternal twin boys. We have a three year old son named Jack. My husband and I like english names. Our short list is:
William (Billy or Will)
Charles (we only have this name chosen for the nickname Charlie, we both don't really like Charles)
names we can't use:
Our last name begins with H and sounds like Harper.
I love the name Henry but I'm unsure how I feel about alliteration ie. Henry Harper.
Any further suggestions would be welcome.
Since you have your doubts about both Henry and Charles, I vote for Thomas and William. They're great together, great with your first son's name, great with your surname, and they have compatible nicknamingness: Thomas/William, Tom/Will.
Another possibility to add to the list is Edward, though I wouldn't use it with William because of Bill & Ted's Excellent Adventure. I like the way it sounds with your surname. Edmund would be a good option, too. Or Simon? Simon and Edmund Harper.