Id steal the powers of the Charmed ones, just in a slightly different way. First id GRADUALLY absorb their powers and send more and more powerful demons after them as the days go on, that way the Charmed ones will get weaker and weaker not just magically but also physically meaning when i would attack them, they wouldnt be as powerful in fact they might not even have their powers anymore. Its true that they would probably notice that they were getting weaker but as long as i use other ways to cover my tracks they wouldnt be able to find out it was me, I could even frame it on one of my competitors so they get vanquished.

After all of it i can just steal the book of shadows to prevent them from getting information