Because of the small size of the group - and the threat before you - another person has joined the group. That makes for six total members, and I think that that rounds it out (as in, no more. All spots are filled). I think you'll find the extra firepower a must down in the tunnels if you run into trouble, though.
dkoz has joined the group. He is playing a sorcerer, which adds another force to the group (leaving only one out, technology).