I'd suggest starting by computing the inverse kinematics/dynamics for each arm independently and seeing if you can place both manipulators where you want.
Of course, there are other calculations that need to be done for a dual-arm system. If you want to hold a particular object with a certain position and orientation, you need to calculate the offset from the object to the 2 points where you're grabbing with each hand. Both forces/torques at each grasping point will result on a combined force/torque on the center of gravity of the object you are holding.
See, for example: https://www.cs.cmu.edu/~maxim/files/dualarmplanning_icra12.pdf
- Sebastian
