But on a serious note, you can't "add" people to your band. However, if you go to the Rock Shop and select "Band", you will see on the bottom right corner of the screen an option to "Change Band Member". By pressing this button, it will toggle between the four members of your band. Here, you can change their names and their looks just like your own created character.
Also, unlike previous games, each default member of the band is associated with a specific instrument. Mr. Lance plays guitar, Nicky plays drums, etc. So you have to make sure you are on the correct instrument ICON when editing a band mate (this is located in the upper right corner of the screen).
It's more simliar to Unplugged than RB2 in that regard.