|Warning: Spoilers are included in this page!|
Isis and Osiris are always found together throughout the existing series. In The Warlock it is finally revealed that Isis and Osiris are Dr. John Dee's masters, and also considered leading Dark Elders. The Elders, under the leadership of Osiris and Isis, set to work on a plan that would ensure that Danu Talis never sank. Dr. John Dee was their primary tool in their plan to change the past. When Dr. Dee failed them, Isis and Osiris declared Dee utlaga - (lat. outlaw), and offered a huge reward for him - alive.
At the end of The Warlock it is revealed that they are the parents of the twins, Josh and Sophie Newman. However, at the end of the Enchantress, it is revealed that they took Josh and Sophie from a Neanderthal camp and 10th century Russia respectively, and are not their birth parents.
They are not actually Elders, but Earthlords, which explains why they didn't Change. They had planned to use Josh and Sophie's power to bring the rest of the Earthlords through time to take over the world, but Josh stopped them using the Four Swords of Power to create the fifth sword, which was actually a hook, and becoming Marethyu.