"It's amazing here, isn't it? I never knew all the odd stuff I could do was magic till I got the letter from Hogwarts. My dad's a milkman, he couldn't believe it either. So I'm taking loads of pictures to send home to him."
-- Colin Creevey to Harry Potter (CS6)
The Creeveys appear to be a close family. Colin took a lot of pictures in his first year because he was sending them home to his father, to show him what it was like (CS5, CS6). As soon as Dennis arrived at Hogwarts, the two brothers became very much a double act, rather than Colin treating Dennis as a two-year-younger tagalong (GF12).
"Creeve" ="to burst," suggesting the Creevey brothers' excitability.