Nobles jumping off the roof, but won't go back up

I have a "tactical" building made of two levels. The first floor is just full of chevals, in hopes that they will be useful soon (ish). It has a stone door on the front with a lock on it. Then there are two curved staircases going to a "roof" edged with parapets. When I get attacked, I enlist all of my nobles and tell them to go to the roof of that building. The last one in locks the stone door so enemies can't get up there without a grappling hook/climbing rope, or destroying the door.

The idea is to get my nobles to use their bows and arrows as the enemies get close and try to break down the door. Otherwise, the nobles like to just run right up into melee range and hit them - where they get hit harder in return! But if I select any one particular enemy, the nobles all jump off the roof to attack the enemies in melee range anyway. No climbing rope to get down or anything, they just jump off like Neo in the Matrix or something.

Once they are on the ground though, they won't go back up unless I assign one to specifically unlock the door for them to get back in. Then I have to watch them closely to see who will be the last one in again (WITHOUT becoming incapacitated, first) and have them lock the door all over again. 

I don't think the nobles should jump off the side of the building like that - parapet or not. They are well within range to use bows and arrows on their enemies, and the ranged option for battle is always enabled. I don't know why they insist on running in to use melee no matter how far away they are. And when they are on that roof, I should be able to target something specific for them to shoot arrows at, while they stay put!