Here are my speculations about who is playing who based on the news announcement that was made:
I am going to presume with my little knowledge on this actors that:
Eva Whittaker will be playing Maraly Weaver, like @starfeather222 said
Billy Boyd will be playing the Overseer (I think someone already said that) or, Claxton Weaver. I’m going to say the latter is more likely
Lesley Nicol will be playing Nurgabog.
Yes I’m aware that each one of these are Weavers. But it makes it even more likely, don’t you think?
Exactly my thoughts! I'm undecided on Billy Boyd; I think you're right, though, that Claxton is more likely. This is going to be epic!