Those are really cool suggestions, Hiara.
I usually try to not
suggest last names for the characters simply because it isn't cannon. When I (try to) write fanfiction, I try to stray from the temptation when it approaches, heheh.
But there was ONE circumstance when we absolutely NEEDED a last name for Eddy, and that was because it was our roleplay and he was going to be married, so it was pretty crucial. However, seeing as we avoided that sort of thing, we never really thought about it, so the suggestion was just winged and thrown out there to get it over with but we look back on it fondly. ^^
Eddy Yenom. Yenom because it's the opposite of Money, which is significant of the roleplay altogether.
So... off the top of my head, if I had to come up with last names for the other two Eds, I would make Edd's something Spanish, and Ed's something German. Couldn't say for the rest of the cul-de-sac kids at the moment. *floats off* XD