Yup Siberys, its a tricky thing DMing. I think eventually with time you will realise that some of your friends will just stay away from D&D in the end (which is not necessarily a bad thing if they jeopardise the campaign all the time).
I am quite fortunate now cos I have managed to break down my old group into people that really want to partake in the adventure and get engrossed into the action and story.
One other thing to make sure is apparent is that ultimately D&D is a dice game and as soon you introduce the risk element back into the game e.g. encounters that will leave half the party unconscious and even the chance of killing a character then they will learn that they will have to focus to enable for their character to survive.
Make then get surrounded or flanked or pn cushioned by those roof top archers. Make them think about their next move otherwise their character will die....pure and simple.
Sometimes you have to make the fear of them having their character die to put them in line. I know they are your frinds but pure and simple they must also understand that there has to be a risk element otherwise why even include battle when there is no fear of dying.
As DM you have certain liberties and I think as your friends they should understand this fact.
Just keep trying things and let me know how it goes.
