I imagine they are using each other but which one has real power?
I expect that the corporate and wealthy individual sponsors of ANTIFA have the real power over both the FBI and ANTIFA. Track the money through the maze of NGOs and "Non-Profit Foundations" and you will find the ultimate sponsors.
Most public officials are minions or decoys. They do what they are told and pass along the orders they are given. The same is true for the ANTIFA and BLM organizers. The prime movers behind all the theatrics do not care one bit about ideology. They are in it for the personal indulgence of unrestrained power over the lives of others.