Could I have different membership plans for different branches?

Of course! That's not a problem at all. Maybe you want to have the main branch on a higher-level member ship plan and have the other two branches on the basic membership plan. The main branch would then be billed according to the higher-level membership plan and the two other branches billed according to the basic membership plan. Of course, remember that their discounts would then be based on what their membership plan is!