If your plants are blooming chances are they'll make their own seeds, but if you want to make sure simply look inside the flower and take the pollen and distribute it on the ends of the pistils of the same flower or on different flowers of the same plant or those of the other plants. Hellebores produce plenty of seed and are often self-fertile. Once pollenated, you will see the seed capsules swell in the interior of the flower. Later they will mature and the follicles will turn from green to greenish-brown before splitting and spilling the seed. This isn't perfect but is generaly what happens with most hybrids.