I fly over and around them, with Volaticus and fire double Acerbatus whenever I get the chance. The same thing works on Weapon Masters, only I like to trick them into throwing their blades the wrong way. s long asyou're quick about flying and firing (to give yourself enough of a buffer0, you can kill the Double Hammers without a problem.
If you have Melio Macir (Hammer) and the Volaticus (Flight) glyphs, you can simply equip double Macir and fly in front of the DHammer with the end of your Macir range and simply alternate between them while inching backwards slowly as they walk towards you. Fastest possible way to kill them without using Hearts