Morgannin09: I'm pretty sure it is possible. Are you saying that you can't take 10 people on the ship? I did a playthrough on YouTube a couple years ago and I took exactly that same crew, except I left Biff behind and took Mario instead, because I wanted to show off his little side quest.
Taking Mario as 10th is possible, if you take Mario the last. However, if you have the same version of Gothic as we do, you can't invite
Morgannin09: Lester, Gorn, Diego and Milten - plus Lares, Lee, Angar, Bennett, Vatras, and Biff
at the same time. As you can see in the ...\PrjGOTHIC\Story\Story_Globals.d, values for Max and Min crew are constants.
const int Max_Crew = 9;
const int Min_Crew = 5;