It takes an action to don and to doff a shield (See Pg 146 of the PHB).
Does that action need to be the PC’s action, Or, could another member of the party (another PC), or even a familiar with opposable thumbs (eg. Imp, Sprite), spend their action to remove a willing player’s shield? What about unwillingly removing the shield from a second player?
Exhibit A: P1 is wedged under a boulder. P2 needs P1’s shield. Can P2 remove P1’s shield as an action?
Exhibit B: An invisible imp sealthily unbuckles the shield of an opponent, right before its master launches an assault. Assuming successful conditions (stealth, strength, slight of hand, etc… check) would the familiar be able to unfasten the shield (action)?