I know he uses dk/shaman and you have a mixed group, but have you watched Hachoo's vid? It's very helpful for placement.

That second wave (I think) up the stairs is the only really 'hard' one (where you get surrounded if you're not careful), on that one just park your guys near the railing so you don't get surrounded. Arthas also can take a little bit of a beating while you drink real fast I've also figured out (I was able to stay out of combat and rez my tank while he was holding 3 dragonkin). He'll heal occasionally, but not enough to keep himself alive. Just drink whenever you can till you can get a good flow going and keep Arthas alive.

It's tough the first couple of times through, but after a few times I've kinda got it on "farm".