Yes they do there is a certain distance they must be from each other to do it. And before you ask if you didnt already know HB does not support party questing. you can level them up using dungeonbuddy together and they will level quickly that way. Problem with that (people recently say otherwise) but i have never found dungeonbuddy to be reliable i have seen my healers stand there two feet from a dying tank not doing anything and i have seen dps fall behind and run into walls. so the only time im willing to do this is if i have 5 accounts to level at once.
Try this then: http://www.thebuddyforum.com/honorbuddy-forum/plugins/leveling/74602-plugin-fix-multibox-suite.html