Ah, my specialty

Since I film all sketches on my own, I have only my clones to talk to
The easiest is to keep the shots short like "clone A - clone B / cut to different angle or close-up of an object / clone A - clone B / cut..."
If you need more of a back-and-forth like "A - B - A" you can have A imagine the lines of B in your head and in editing do a
slight adjustment of the speed during A's reaction.
If it needs to go on even longer, you can play back the already recorded audio of one clone for the other. That still takes a lot of practice though.