Samuel Isaac "Sam" sounds good to me for the DS.
I'll take your offer of David Thaddeus for the DH, but I really really really hate the nickname Dave.
I don't really like Eydis Anais, though. I don't even know how to pronounce it, to be honest. How about something like Juniper Calista?
As for the surname, as I said before, I don't really care. So our of those choices, I'll go with De Witt since it isn't so monosyllabic.