Well, the Roland CII is actually a pretty good 2 seater. I'd give it another run. Try to give your gunner reasonably good, stable lines of fire and you should do OK, of course, one on two vs. Nieuports isn't really fair. You really can't out-turn them, so try to turn like a snake, when you turn right, wait for them to turn right and then quickly go left. As they come around, wait until they are committed and go right again. This will hopefully shake them off your tail for a few secs and give your gunner a fair shot. I also skip a few days after every mission in my careers to simulate the boring, uneventful missions because when I'm flying, I like some action. That may help that DI show up a little sooner!
Good luck and report back with results!