That is a good question. No, you dont have to take all three for both. In my opinion, the most you would have to take is Step 2 for both, but I may be wrong.
It really depends on what you want to go into, to determine if you really need both tests. Different people will give you different answers on this topic, which I am sure there is a thread somewhere on here.
I myself am going into primary care in the midwest, so I am only doing COMLEX.
Hope that helps
Chris