"One lamp needs two ballasts"
Really? Why....
I read a post in a garden forum once about souped-up fluorescents running off of two ballasts for DIY grow lights, but they were T-8's instead of T-12's or T-5's and didn't last very long running off of two ballasts. (FYI, the T-number refers to diameter of bulb in eights of an inch. ex. T-5 means the bulb is a nominal 5/8" in outside diameter)
But google is your friend here, the answer is out there. The answer probably will make sense once you understand "series" and "parallel" wiring schemes.
Good luck!
Stan