Enforce the sterile cockpit -
No non-essential conversation below 10,000' and nothing within 1000' of a target altitude.
If they still wish to talk, remind them about the sterile cockpit and if they STILL want to talk, then you can just ignore them for anything that's not flight related. I know it may be difficult to do, but if you stop responding (no head nodding either!), they will stop talking - Everyone eventually gets the message.