If you already know the basics of Timeline it shouldn't be difficult to do that.
Interpreting what you mean by loose arm, if you mean it completely loose, dead like, with no control just physics from the body, then you can set triggers for the control points to be off (position state and rotation state), then on again when you need it animated. I take it you know how to move body parts with Timeline animation, so moving a arm to the head of the other person should be easy.
You have at least 2 options to grab and hold a person's head. You can parent/physics link the hand to the head, or the other way around, so that the movement of one pulls the other. The control points change to PL is done with triggers like the above.
Alternatively you can make one's arm movement sync with the other's head movement, and with the right timing it gives the impression of the same grab and pull action. On the first one the physics involved might need tweaking to get it right, on the second you need to time it right.
Is this enough to give you an idea on how to do it in Timeline?