What you want to do is add a simple prop such as a box. With IK for the Hand turned on constrain the hand to the box. There will be a new dial created for the constraint, when turned to 1 the hand fully follows the box, when 0 then to returns to its original pose. You then constrain the box to the handle. There are adjustment controls to align the box to the handle and the hand to the box. Make adjustments till you get the movement you want. Holding hands is done the same way except constrain both hands to the prop and then as you move the prop back and forth it will look like the couple is swinging their hands in time.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13