A control principle common to karate's kote-gaeshi lineage and Filipino gunting: whoever controls the elbow controls the weapon.
Neutralize the blade by trapping the weapon arm at the elbow and shoulder joints.
Once you are on the outside line, place both hands on their weapon arm. Near hand cups the wrist; far hand cups the elbow from underneath.
Draw the elbow into your chest and pin it there. Their shoulder now has nowhere to reorganize without moving their entire body.
Rotate their palm skyward. The wrist rotation collapses their grip, and the blade often falls on its own. Strip, strike, or walk them off balance, but never release the two-on-one until the arm is empty.