So as an update... I never got around to messing with nicknames. Once I got it up and running, it has just been too much fun playing to mess with mods The kids got used to using their "legit" usernames no problem. The tekkit launcher is fickle with saving their username. One of the kids I don't think their user has ever disappeared, but the other kid it seems like half the time when the launcher opens, his saved login is gone. So I had to dumb down the passwords which makes me a little uneasy. Their usernames are pretty close to just their first names, but they do comment on my name all the time but I guess it doesn't matter. In all, the transition was pretty non-eventful and they are really into building the machines, although they are too impatient to save up resources for the more complicated ones. The older one is one diamond away from building a quarry, though, but he keeps going back to playing singleplayer in creative mode :/