From my experiences, I've found that issuing an order to party members to hold position will be enforced provided I don't return to controlling them and they don't move at all after the order was issued (i.e they hadn't quite skidded to a halt yet or were bumped out of place by someone moving into them etc etc).
So if I select a party member, have them stand perfectly still away from anyone else, click hold position and move to another party member, they will stay there until I go back to controlling them, so long as I don't let anyone bump into them. To get them to move freely again, I just move them a step in any difrection and that seems to break the Hold order when I move off them.
The exception to this is my own character (i.e The Inquisitor). I can't get my character to Hold Position for love nor money. So on puzzles that require people to be in multiple places, I make sure my Inquisitor is the free roaming one and/or last one to get into position. In combat it seems useless, because people are bumping into each other and flying about from explosions etc and that seems to break the Hold order completely. As does archers trying to re-establish LOS etc - its just chaos.
Out of combat, it sort of works if I stick to the above method, but it is a really fiddly system. I generally don't use Hold Position at all in this game, and I used it all the time in the previous 2 games.