I plan to create a Dual-branch air-handling unit (attached) for building energy model. As we know, there are some restricts of the node settings in the HVAC system by using EnergyPlus or OpenStudio. Whether there are some methods like using EMS to create the system? 
Are you trying to model a dual duct system (hot branch/cold branch)? That is an available system type in OpenStudio/EnergyPlus.
Otherwise you cannot define multiple zone terminal units serving the same zone from the same air loop.
In my case, some return air (RAB) will be used for reheating the cooled air from cooling coil directly. Is it possible to create two branches for return air? Thanks.
nope, this is not possible in EnergyPlus.
I'm wondering if you could approximate this with a VAV AHU with series fan powered boxes. That also can have return air (in the case of SFP boxes it is local plenum air) used for reheating the cooled air from the cooling coil. You would just need to think through what you would need to hard code to make it work like you want.
For example, if your system is constant volume and only has two fans but more than two zones, you would need to set the main primary fan to have zero power and a minimum flow fraction of 1.0 and spread the SA1 fan power evenly between your interior zone SFP terminals and SA2 fan power evenly between your exterior zone SFP terminals.
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