The form variables are global to the process.
The problem is if you use a xfaForm variable, you have to point to the xdp the variable is going to use. If you use three different forms, you'll need three different xfaForm variables that points to the three xdp.
Now, when you configure the xfaForm variable, you have to configure a render service that takes care of rendering the xdp into a pdf. That render service has a data parameter that contains the data you want to merge.
What you can do is have an xml variable that will contain the latest data and use that for the data parameter of the render service. When a user submits the form, you can use a SetValue that takes the data from the xfaForm into that xml variable. You would need that SetValue after each user step in each branch.
Does that make sense.
Jasmin