Well then, apparently we have seven trolls as a pipe-opener. If they would kindly oblige by passing through some reasonably heavy undergrowth, I'll start the ball rolling with an Entangle and hope to slow them down a little. Then follow up with a Faerie Fire on as many as I can get - which will be one, or two at the outside (three man-equivalents). We'd better concentrate on one as much as possible until it goes down - anything that can slow them down in the meantime would be well worth doing. I will go to bow after the spellcasting.
If we have a few minutes' grace, Gwaelur is no doubt the most expert aid we could give to Bitur.