KCL using phasors: how should we proceed knowing effective voltage/current
No full solutions for homeworks, only quidance. See the following image:



The phasor of -I3 is as long as the phasor of I3. Think different possible directions for the phasor of the 2A current. Decide the maximum and minimum lengths for phasor -I3 when the angle beta varies. 

There's no need to think varying directions for the phasor of the 1A current. Angle alpha can be fixed because the image can allways be rotated.One angle in the system can be arbitary.