The composite optical vortices (OVs) in the superimposed field of two parallel, off-axis flattened Gaussian vortex beams with topological charge m1, 2=±1 at the waist plane and their propagation dynamics in free space are studied. Detailed numerical calculations and analysis show that the number, position and net topological charge of composite OVs depend on the control parameter, such as the relative phase, amplitude ratio, waist-width ratio, relative off-axis distance, beam order, and on the propagation distance, but the topological charge is not always conserved.