I'm not sure if I understand clear.
I imagine your animation:
*Figure moves/fencing right hand parented to the sword (hands is translated along the sword moves). In one moment for example frame X figure is taking sword to left hand and fence with sword in left hand.

*-Make your animation from 0 to X frame with right hand parented to sword 1.
-At frame X pose left hand holding sword.
-select sword 1 on properties window, click copy (ctrlC) and make sword 1 unvisible
-seclect sword 2 make it visible, on properties window, paste (ctrlV) and parent left hand to sword 2
-Animate sword 2 in next frames. Left hand should go follow it. Of course forearm, arm etc should move follow.

When you finish your animation turn off IK. Check animation again what is broken. Most often you must change 1st frame only changing twist or bend or side-side parameters adding/removing 360. For example if twist param=210 change it for -150 (210 - 360 = -150). Hand should stay in the same position.
When your animation work correct with IK off it is ready to be saved or exported.