Add the following text to the description of the unarmed weapon group:
“Unlike most weapons, an unarmed weapon does not occupy the hand wielding it. This means you can perform actions and benefit from effects that require you to have your hand free (or empty) without removing the weapon. However, you can also only attack with the unarmed weapon while your hand is free, unless you’re attacking an enemy whom you are currently grabbing with that hand.
This does not allow you to wield more than one weapon or implement in a single hand, even if both are in the unarmed group. You can choose to wield another weapon or implement in a hand that currently wields an unarmed weapon, but while you do so, you lose the ability to wield that unarmed weapon.”