Kk, that should be plenty of gear and people. I'll take another look at Corniav's delays when I get a chance. I scaled his timer up a bit from the default in the first round of tuning, but there may be some other issue that's borking things up.
For the Rathe, generally, the trick/strat is that the non-mezables do much less damage as their hp lowers, so once one is almost dead, he's easy to offtank (lowest level only hits for 100ish iirc), and then you can fetch another and repeat. Then you can kill them practically all at once and just have the mezables to deal with. On live, we'd beat down and mez the mezables first, but that's probably not as necessary here.