For the primary W/O emulsion, we should probably use a high pressure homogeniser or a rotor-stator device at high speed. These techniques create relatively high shear (especially the high pressure homogeniser) so the required droplet size can be reacher. Then, for making the final W/O/W emulsion, we need a milder technique, otherwise the emulsion will be damaged. A rotor-stator homogeniser used at low speed could work, or (better) premix membrane emulsification.