About the twitchy steering: I have a Co-Motion, which is one of the quicker-steering tandems, and I have found that stokers make the most difference. I am used to very quick steering on my single, but having someone else providing "input" is disconcerting. So it is important to train that stoker to ride "quiet". Then, I think you just need to ride it a bunch, and you will become comfortable with it. As a last resort, you could get a fork with more trail. But I would ride a lot before I decided on that.